All language subtitles for Universe

Our universe is a place
of infinite variety.

Two trillion galaxies...

..billions and billions of stars...

..and countless planets,
worlds beyond imagination.

The universe is so vast,
so incomprehensible, so terrifying,

that I think it's quite natural for
us to choose to live out our lives

completely oblivious to it.

Perhaps that's why there's a sense
of relief that rises with the dawn.

The brightening sky hides the stars
and the questions that they pose.

After all, they are
the biggest questions.

How did the universe come to be?

Why are we here?

And how will it all end?

We have to face those questions
if we're ever to acquire

a truly deep understanding
of ourselves.

You see, astronomy challenges us.

From one perspective,
we're just grains of sand adrift

in an infinite and
indifferent ocean.

But from another perspective, we are
nature's most magnificent creation,

collections of atoms that can think
and wonder about the universe

and choose to explore it.

OVERLAPPING LAUNCH COUNTDOWNS

We have liftoff... Zero...

In our quest for answers, we're
venturing ever further from home,

far beyond the planets...

..and out to the stars.

Our spacecraft are sending back
a stream

of extraordinary revelations...

..visions of alien worlds...

..with the ingredients
to create life.

We've seen galaxies collide...

..black holes devouring
star systems...

..and we may have glimpsed
the origin of the cosmos itself.

With every new observation,
every new piece of knowledge,

there is the opportunity to acquire
a deeper understanding.

And as we answer question
after question, we get ever closer

to being able to tell what is surely
the greatest story ever told.

# Take me away. #

Nasa's Parker Solar Probe,
a daring mission to shed light...

..on the mysteries of
our closest star.

This is a journey into
never-never-land, you might say.

Nasa's Parker Solar Probe is the
first spacecraft to touch a star.

It's designed to fly through
the sun's atmosphere...

..braving temperatures no spacecraft
has ever endured.

The Parker Solar Probe
is allowing us to know our star

as we've never known it before.

And it's also helping us to tell
the story of all the stars.

Our sun is from a long line of stars
dating back to the dawn of time...

..from fierce blue giants...

..which first lit up the universe...

..to later generations...

..whose deaths enriched the cosmos
with precious elements...

..the building blocks of
our solar system...

..and allowed our sun
to create the thing

which brings meaning to
the cosmos...

..life, you and me.

We have a strange relationship
with the stars,

somewhere between awe
and indifference.

I think we take our star,
the sun, for granted,

partly because of
its predictability.

Every day, it rises in the east
and sets in the west...

..without any help or reverence
from us.

But many ancient cultures
deified the sun.

They treated it as a god.

And the sun gods were creators
and destroyers of worlds.

So which is it?

Well, I think that the modern story
of the stars, as told by science,

which is indisputably an epic story,

stretching back over 13 billion
years to the origin of the universe,

places them firmly in the realm
of the gods.

If we want to understand
where these gods came from...

..we have to go back...

..to a time before the stars.

In the beginning,
the universe was dark.

But it was not empty.

Something was lurking in the void...

..stretching out tendrils.

The cosmic web grew to become
a vast structure...

..crisscrossing the entire universe.

It was formed by interlocking
filaments of dark matter.

And it was at the places
where these filaments met...

..the intersections...

..that the first stars, our sun's
earliest ancestors, were born.

The cosmic web is the scaffolding
of the universe,

the vast and intricate structure
that spans the void.

The web is made primarily
out of dark matter,

a mysterious substance
that dominates the universe,

although we don't know what it is.

It's one of the great mysteries
in modern physics.

It's probably some kind of particle

that interacts very weakly
with itself and with light.

It doesn't interact with light.

You can't see it, which is why
it's called dark matter.

But it does influence the universe
through its gravity.

It was in the dark heart
of the cosmic web

that gravity began to sculpt
the early universe...

..drawing together the two simplest
elements - hydrogen and helium...

..the raw material
for the very first stars.

Hydrogen gas clings to
the filaments of the web,

attracted there by the gravitational
pull of the dark matter.

And where those filaments cross,
the gas can become dense enough

to collapse under its own gravity
to form great clusters of galaxies,

each filled with billions of stars.

The universe was approaching
a turning point.

Hydrogen and helium
poured into the regions

where the filaments crossed...

..gathering into ever denser clouds.

Gravity asserted its grip...

..and the clouds of gas
began to collapse...

..becoming denser and denser.

And in the densest regions,
the gas became so hot...

..that nuclear fusion
reactions began.

And out of the maelstrom...

..the first gods emerged.

And there was light.

The stars illuminate the universe.

But that is the least interesting
thing that they do.

The thing that makes
the universe interesting,

that brings meaning to the universe
is that -

life, you and me.

And life is just chemistry.

And chemistry requires
complex chemical elements.

The only thing that existed
in the universe before the stars

was hydrogen and helium.

Life requires carbon and oxygen
and iron.

All those things were made
in a process called nuclear fusion,

in the cores of stars or even,
for the heavier elements like gold,

in the collisions of stars.

So, without the stars, the universe
would be uninteresting.

It would be meaningless.

It would be just an infinite
box of gas.

The first stars were monsters...

..hundreds of times as massive
as our sun.

They burnt with such ferocity
that they shone blue...

..with surface temperatures
in excess of 100,000 degrees.

They were the largest stars
ever to have lived...

..violent and volatile giants.

A star is essentially
a balancing act.

The force of gravity
is constantly trying to collapse it,

and that pushes its ingredients -
primarily hydrogen, single protons -

closer and closer together.

Now, when those protons
get close enough together,

another of the fundamental forces
of nature, the strong nuclear force,

takes over and it can stick
the protons together.

That releases energy, which creates
a pressure which holds the star up.

Now, the more massive the star, the
stronger the inward pull of gravity,

and the more energy has to be
released to maintain the balance,

and so the faster the ingredients
are used up.

..fighting the relentless
pull of gravity...

..consuming more and more
hydrogen fuel

to maintain their
precarious equilibrium.

For most of its life,
a star burns hydrogen -

the simplest chemical element,
with one proton in its nucleus -

into helium, with two protons.

Now, when it runs out of hydrogen
in the core,

the core starts to collapse
and heat up,

and the star responds by building
ever more complex elements.

So it makes carbon,
with six protons,

and oxygen, with eight protons,

releasing more and more energy
as it goes.

But when the star has assembled iron
in its core,

with 26 protons in its nucleus,

no more energy can be released.

The star loses its battle
against gravity.

It collapses

and in a final moment
of creation,

salvaged, if you like,
from its destruction,

it distributes those newly minted
heavy chemical elements

out into the universe.

Imagine we could journey back
in time

and watch the first star live
out its brief, luminous life.

After only a million years,

the star used up all of its fuel...

..the core collapsed...

..the star imploded...

..and then rebounded
in a colossal explosion -

a supernova.

In death, the first stars began
to transform the cosmos,

enriching the ocean of hydrogen
and helium,

which filled the
universe with heavy elements,

to build new generations
of more complex stars.

Over time, these elements
gathered together...

..creating rich clouds of gas
and dust.

Nurseries where new generations
of stars were born.

And not just stars,
but families of stars -

the first galaxies.

And around this time,

some of the early star systems
formed

in our own galaxy,
the Milky Way.

A new age of complexity
was dawning in the universe.

Now there were stars of
different sizes...

..and different colours...

..and, crucially,
new bodies had appeared...

..planets.

Places where the rich chemical
elements

built by previous generations of
stars could finally find a home.

Countless billions of stars
have come and gone

since those first giants illuminated
the darkness,

each enriching the universe
with the material

out of which the next generation
formed.

Blue stars and white stars,
single stars,

double stars, even triple star
systems orbiting around each other.

The conditions were now right for
those stars to drive the universe

into a new and profound
age of complexity.

Our Sun was formed from the ashes
of generations of ancestors.

Just one small star in a galaxy
of billions of brilliant gods.

For the first million years
of its life,

the Sun was virtually alone,

wreathed in clouds of gas and dust.

The dust slowly clumped together...

..forming clusters,
the size of pebbles,

then boulders...

..and finally...

..planets.

But the planets were lifeless rocks.

Only the Sun had the power to turn
them into worlds.

Some were too far away from the Sun.

Ice giants -

frozen, seemingly, into infertility.

Others formed too close to the
Sun,

seared by a relentless light.

They became scorched desert worlds,

but there was a planet in the Sun's
family

that quite by chance formed neither
too close nor too far away.

An arcadia, where our star could
breathe life into dust.

The planets are just the leftovers
from the formation of stars.

The sort of debris, if you like.

It's just little specks orbiting
around those magnificent flames,

but the planets are also the
places in the universe

where gravity has concentrated the
heavy elements

built by previous generations of
stars.

And that makes the planets
the canvas

on which the stars can create.

The canvas on which the stars
can create,

what do I mean by that?

Well, just look around.

Everywhere you look on Earth,
there is complexity.

Not only mountains and rivers,

but living things, animals and
plants, human beings,

human civilisation,

the most complex thing we know of
anywhere in the universe.

So you have to ask yourself,
how can it be that such complexity

can emerge completely naturally
in the universe?

Well, the answer, in fact, was known
in the 19th century,

and it comes from the science of
thermodynamics.

In the 19th century,

people were interested in the
efficiency of steam engines,

and steam engines are, after all,
the machines that powered

the factories that allowed people to
build increasingly complex things.

And it turns out that the only thing
that matters for a steam engine,

the thing that determines its
efficiency,

the thing that allows it to do work
and build things

is the temperature difference
between the fire,

the furnace
and the heart of the steam engine

and the cold environment
surrounding it.

In the universe, the stars
are hot spots in a cold sky.

We are sitting, in a very real
sense,

inside a giant steam engine, powered
by the furnace of the Sun.

And it's in that sense that the
stars are the creators

of complexity in the universe.

But creating complexity
is a subtle art.

You need an engine -

in this case, a star
that's not too wild and flashy.

A star which is consistent enough
for long enough

to kindle
the sparks of life...

..and allow those sparks to flicker
and flourish.

The most important property
of a star,

if it's to nurture a civilisation,

is magnificent dependability.

No-one knows exactly how life
on Earth emerged...

..but what we do know is that at
some point,

primitive cells living in the ocean
began using the Sun's energy

to power life-giving chemical
reactions.

These cells formed a bridge
between Earth and Sun,

delicate engines which harness the
fires of our star,

using sunlight to turn carbon
dioxide and water into food.

This process,
known as photosynthesis,

unleashed the Sun's creative
power...

..and drove the evolution
of complexity...

..from primitive bacteria,

to plants and trees...

..and,
ultimately,

to you and me.

Photosynthesis is a process that's
very easy to describe in words.

The plants take energy from the Sun

then use it to react carbon dioxide
and water together

to make sugars and a waste product,
oxygen.

Really easy to say.

Very difficult to do.

I mean, there's a part of
that photosynthetic machinery,

everything you see here,

every plant on the planet's
got a photosystem, too.

It's comprised of 46,630 atoms,

all working together in an intricate
machine.

Very efficient. It took billions of
years of evolution.

Then we eat the plants, or we eat
something that's eaten the plants

and we do the reverse reaction.

We take those sugars and we breathe
in that waste product, oxygen,

react them together, release a bit
of energy,

a bit of the stored sunlight,
if you like,

and we use that energy to maintain
our structure,

to grow, to live.

Trillions of stars have existed
since the universe began...

..but ours has nurtured that most
miraculous thing,

life.

And that makes the Sun
a truly remarkable star.

That is the only star we know
of

anywhere where there are collections
of atoms in orbits around it,

you and me,

that have named
it.

The Sun, our Sun.

We've worshipped it, deified it
since the dawn of history.

In fact, it's been argued
that the Sun lies at the foundation

of all religion, and there
may be some truth in that.

In fact, I think there is a deep
truth in that,

because we all owe our existence,

this brief time we have in the
universe,

to that star.

In fact, in a deeper sense, to all
the stars.

We don't need to invent imaginary
gods to explain the universe.

We can replace them with
the real thing.

Everyone we love...

..everything we value...

..our supreme accomplishments
as a civilisation...

..were created and crafted...

..by stars.

There are over 200 billion
stars in our galaxy...

..and there are two trillion
galaxies in the observable universe.

We're living in the Age of Stars...

..an era of light and life
in the cosmos.

From our fleeting human
perspective, stars seem eternal...

..but even gods are not immortal.

Where there is light,

there is darkness.

Stars are creators...

..but they can be jealous
guardians of their creations.

Many smaller stars don't die
in spectacular explosions,

instead, they slowly.
fade away.

They hang on to the precious
elements they made,

becoming fossil stars...

..and as more fossils
litter the universe,

more life-giving elements
remain locked away,

starving the cosmos of the material
needed

to make new generations of stars.

The Age of Stars may seem infinite,

but it had a beginning

and it will also have an end.

Imagine a timeline of the universe

and imagine that this is the origin
of the universe,

the Big Bang,
13.8 billion years ago.

After 100 million years
or so, the first stars formed.

On this scale, one centimetre
is about 20 million years.

After four billion years, the peak
rate of star formation occurred.

The maximum number of new stars
were born.

After nine billion years,

our Sun was born.

And today we stand,

13.8 billion years later,

about halfway
through the lifetime of our Sun.

Now, in about five billion years'
time,

our Sun will die, but new stars
will be born

and many of the oldest
stars in the universe,

the smallest stars,
will continue to shine.

In fact, we think that the last
star will cease to shine,

the universe will go dark,

in around ten trillion years.

On this scale, that's about 5,000
metres away from the Big Bang.

But that's not
the end of the universe.

As far as we know, the universe
will continue expanding forever.

And so the Age of Starlight
is the briefest moment of time

in the infinite history
of the universe.

The Age of Darkness will go
on and on and on.

Stars won't just disappear,
of course.

They'll be here for aeons to come.

But over time, the universe,
will grow darker,

colder
and emptier.

There are stars around today
that existed

close to the beginning
of the Age of Stars...

..and some of them
will also witness the end.

They're the longest lived
stars in the universe,

red dwarfs.

TRAPPIST-1 is one
of these ancients.

It's already more than seven billion
years old,

almost twice as old as our Sun...

..but only around a tenth
of the size...

..and less than 1% as bright.

It's a cool star,
slow-burning...

..and that is the secret
of its longevity.

Because they burn slowly,

red dwarfs live
for a very long time...

..far longer than any other star.

Like the Sun, TRAPPIST-1
has its own planets -

seven rocky worlds,

each roughly the size of Earth.

Some may have atmospheres

and even oceans...

..but there the similarity ends...

..because these are strange worlds.

Every one of these planets
is locked in its orbit,

one side facing TRAPPIST-1,

the other side frozen,

permanently exposed to the cold void
of space.

If you could stand on the surface
of one of these ancient worlds...

..as the aeons passed...

..you could watch the future
of the cosmos slowly unfold.

And one day,
five billion years from now,

you'd see our Sun flicker
and fade away forever.

The death of our Sun will
probably go unremarked.

We had hope that we'll be
around to see it.

Maybe some alien astronomer
on a world far away

across the Milky Way will see it
through the end of their telescope,

but I don't think they'll give
it a second thought.

We've seen hundreds of stars
die

and we don't give them
a second thought.

But I think the death of our Sun
will matter here locally

in this little corner of the galaxy,

because it will mark the end
of a glorious time

in the history
of our galaxy,

where meaning, where science and
literature

and art and poetry and
music existed here.

And that does matter.

Why does meaning
have to be eternal?

It's the fragility of our lives
that makes them valuable.

I think the wonderful thing
is that our star

has taken the laws of nature here on
this planet

and crafted such a
magnificent expression of them.

You, me and all this.

Stars like TRAPPIST-1 will linger on
long after the death of our Sun.

We will never know the name
of the last star...

..but we know that the last star to
shine...

..will be a red dwarf.

The last star will slowly cool

and fade away.

With its passing, the universe
will become, once again,

a void,

without light

or life

or meaning.

The stars illuminate the universe

and create its most intricate
structures,

and one day they will all be gone.

The stars are gods,
but they are mortal gods.

And when that time comes when
the last stars have faded

and all possibility of life
and meaning in the universe

has faded with them,

they will have left the most
profound legacy

because for a moment in the long
history of the universe,

the stars illuminated the dark

and allowed us
to illuminate it, too.

MUSIC:
Who Knows Where The Time Goes?
by Fairport Convention

# For who knows
where the time goes?

# Who knows where the time goes? #

We want to study the Sun because it
teaches us a lot about stars.

It teaches us a lot about all
the other millions and billions

of stars in our galaxy and beyond.

There was a moment when we were
putting the spacecraft together

that I just took a moment and looked
at the spacecraft

and realised
this is going into a star.

And to realise how special
it was

to be able to have worked on this

and that humanity decided this was
something we wanted to do.

Status check.

Go, Delta.
Go, PSP.

Minus 15.

Launch night,
I was sick to my stomach.

Five, four, three,

two, one,

zero.

Liftoff of the mighty Delta IV
Heavy rocket

with Nasa's Parker
Solar Probe.

There we go.

The spacecraft is the first that
NASA has named after a living

person because Eugene Parker is
really such, you know,

an eminent physicist in our field.

The Delta IV Heavy is a very
slow rocket

compared to the other launches I've
seen,

so I just saw fireballs and was
very, very frightened for a while.

25 seconds into flight.

Temp pressures continue to
look good on all three boosters.

Then realising that this was all
OK,

as it slowly made its way
up into the sky.

Now, 50 seconds into flight.

Parker Solar Probe is so
revolutionary

because it's the first time that
we're actually going in

to touch the Sun.

We're going 94% of the way from the
Earth to the Sun

to actually experience the
solar corona, the Sun's atmosphere.

I think at closest approach,

it'll be about eight solar
radii from the Sun,

which is just mind-blowingly
close.

So we were expecting things
to be very hot,

over 2,500
Fahrenheit,

but in a soup of a million
degree plasma.

That's a real challenge
for the spacecraft

to survive that environment.

So in order to do that, there's
a very large heat shield

on the front of the spacecraft,

which protects the majority of the
instruments

which are sat
behind on the spacecraft body.

What makes Parker so great
is the fact that it has a set

of instruments that work together
in order to look in all directions,

in order to solve those big
mysteries about the solar wind.

The solar corona has been mysterious
to us since we've known about it,

so it's a very strange thing.

The surface of the Sun is sort
of 6,000 degrees,

and then above that, you have this
very thin atmosphere

that's a million degrees,
super hot.

And the way that's heated, we know
it has something to do

with magnetic fields, but we don't
know exactly how it works.

That's where the solar wind
is generated.

We don't know quite exactly
how that works, either.

Other things that have come out of
this are coronal mass ejections.

When we originally did the proposal,

we were thinking that we would see
five

in the entire seven year
mission, if we were lucky.

We ended up seeing around four
to five in the first year,

so there has been just a total
switch

in terms of how active the
Sun is

or what we classify as
coronal mass ejections.

Maybe a little bit of both.

It is a joy to see all the data
coming back.

It's a joy to share it with others

and to see them be as curious
as I have been for the last decade.

So Parker's just begun its mission,
really,

and it's already really started to
truly transform our understanding

for how the Sun works.

Next time...

..we had deeper
into the galaxy...

..on the hunt for alien worlds...

..and perhaps the first signs of
life.

Journey through the universe
with the Open University

and learn more about stars, planets
and galaxies with this free poster.

Order your poster by calling...

Or go to...

and follow the links to the
Open University.

MUSIC: Who Knows Where The Time
Goes? by Fairport Convention

At this precise moment
on a planet far, far away...

..an alien sunrise
ushers in a new day.

But will alien eyes gaze upon it?

Or will it go unseen?

Just another moment in a vast,
sterile universe?

The hunt is on for the answer.

Magnificent desolation.

Beautiful, beautiful!
Ain't that something?

# Take me away. #

The Milky Way...

..hundreds of billions of stars...

..spread across 100,000 light-years
of space.

Among them, the sun...

..with eight planets orbiting
around it, including our home.

Until very recently, these were
the only worlds we knew of,

the only planets we could hope
to explore

for signs of life beyond Earth.

When I first got into astronomy back
in the 1970s,

we knew of no planets beyond
our Solar System.

We didn't have the technology
to detect them

even if they were there.

Our neighbourhood was the only place
we could look for life.

And so the hunt for life began
in our own backyard.

Over the last few decades,

multiple missions have explored
our Solar System's planets...

..and even some of their moons.

But to date, even as we continue to
look, no convincing evidence of life

has been found on any of
these worlds.

Earth remains one of a kind...

..the only living world
around the sun.

But as the exploration
of the Solar System continued,

another search had begun...

...for worlds that lie
far beyond these shores.

You know, the wonderful thing
about astronomy is that

as we develop better and
better technology

and accumulate more and more
knowledge about our universe,

we turn more and more of these
points of light in the sky

into worlds.

I mean, that, we've known is a world
for a long time

because that is the planet Mars.

But just above Mars tonight
is a constellation called Pegasus.

This is the Square of Pegasus.

And we now know that around there
is a star called 51 Pegasi,

which has a planet
orbiting around it,

a gas giant about
the size of Jupiter

that goes round that faint
point of light every four days.

It is wonderful to think
that in my lifetime -

in fact, in my adult lifetime,
in the last 25 years -

we've gone from a universe

that could have been devoid
of planets beyond our Solar System

to a universe that we know
is teeming with places

that we can search for life.

Over the last three decades, some
of the most powerful telescopes

on Earth have joined the hunt...

..searching for planets
unimaginably far away...

..hiding in the dark.

Planets like 51 Pegasi b...

..the first world outside our
Solar System to be detected

around a sunlike star.

51 Pegasi b is a gas giant,
around half the mass of Jupiter...

..but far closer to its star.

Just imagine what that world
might be like...

..a world with skies
torn by titanic winds...

..where its hot interior
is bathed in rain of sapphires.

In every sense, 51 Pegasi b
is an alien world.

And we soon discovered that
the galaxy is full of planets

unlike anything seen in our
Solar System...

..planets enveloped by
fierce radiation...

..their surfaces
battered and stripped

by the high-energy strobing light
of their star...

..worlds so cold, their atmospheres
have frozen solid...

..or great swollen planets...

..with the density of Styrofoam...

..and fathomless atmospheres.

These discoveries proved that, in
one sense, we really are not alone.

There are other worlds out there
waiting to be explored.

We estimate that
in the Milky Way galaxy,

there are more planets than stars -
hundreds of billions of them.

That's hundreds of billions
of places to look for life.

But there's a catch, because not
all worlds - by a long stretch -

are like this one.

The first planets we found
appeared too bizarre, too large

and often too close to their stars
for living things to survive.

To find worlds where life
could exist, we needed to look for

smaller, rocky planets
in orbits further from their stars.

MISSION CONTROL: T-minus 10,
9, 8, 7...

We needed to look for
another Earth...

..3, 2...

Engine start. 1, 0, and liftoff
of the Delta II rocket with Kepler,

on a search for planets
in some way like our own.

..so the hunt moved to space

with the launch of Nasa's
Kepler Space Telescope...

And we have separation.

..searching for Earth-like worlds
in the galaxy beyond.

Kepler crossed 94 million miles
of space...

..until it arrived
in a steady orbit around the sun...

..from where it looked out
with a fixed and clear gaze...

..to a single patch of sky
in the constellation of Cygnus.

Exposing its sensitive
light meter...

..to the light of 150,000 stars...

..it began to look for Earth-like
alien worlds.

Kepler doesn't detect planets
directly. They are far too small.

They're just specks of dust
relative to their parent star.

They're also very faint.

They don't emit light of their own,
so they just glow very dimly

in the reflected ambient light
of their stars.

So, Kepler has to detect
planets indirectly.

Imagine that a moth just flew
across the beam of light

from the lighthouse.
Now, I wouldn't see the moth,

but if I had
a sensitive enough detector

and everything
was lined up properly,

I might just see the brightness
of the light dim.

And that is how Kepler
detects planets.

We imagine there's
an alien astronomer

in some distant solar system
looking back at the sun,

and everything's lined up
so they see the Earth

trace across the face of our star.

They would see the light from
the sun dim by one-hundredth of 1%.

It's a tiny amount, but it's enough.

And if they saw that dimming
was regular,

if they saw the star dim
once every year, in this case,

then they would infer that there's
a planet orbiting around a star.

With its exquisitely sensitive
light meter...

..Kepler sees only the regular
dimming of pixels...

..just a few bits of information.

But from those bits, astronomers
can begin to build a picture

of the worlds
that dim the starlight...

..worlds that might, in some way,
resemble our own...

..worlds like Kepler-36b.

The planet was one of Kepler's
earliest discoveries.

Orbiting a star similar to our own,

we'd found a world that, at first
glance, might seem familiar.

Weighing in at around four times
the mass of our own planet,

Kepler-36b was one of the first of
a new class of planet -

a super-earth.

The Kepler data doesn't just
allow us to say there's a planet

around that star. It allows us
to characterise those planets.

So by looking at the precise way
that the light fades

and then rises again,
and the timing between the dips,

we can measure the orbits
of the planets.

And if there are multiple planets
in the system,

we can even estimate their masses,

so the Kepler data allows
astronomers to paint a picture

of the worlds it discovers.

But the more detailed our picture
of Kepler-36b became...

..the less Earth-like
this super-earth appeared to be.

It orbits very close to its star,
circling once every 14 days.

And it has company...

..a gigantic gaseous companion...

..with an albeit unusually close
to its smaller sibling.

The proximity of both its star
and sister planet

allows us to imagine
the bizarre conditions

that may exist on the surface
of Kepler-36b.

The planet may be tidally locked,

which would mean that one hemisphere
always faces the star.

On this side, the punishing heat
could turn the ground molten...

..creating rivers of lava
that would crisscross the surface.

The planet could experience
violent eruptions...

..as the gravitational pull
of the gas giant

triggers intense volcanism...

..each time it passes by.

But Kepler-36b could also be...

..a planet of ice.

Because if it's tidally locked,

the far side would face permanently
away from the star...

..and we could imagine
a freezing cold hemisphere

shrouded in eternal darkness.

For now, this is all just
informed speculation.

But we are beginning to build
a picture of these worlds.

I mean, imagine a world where
the sun stays at the same point

in the sky forever,

so one side of the planet
is in eternal night

and the other side in eternal day.

And even the twilight strip
between day and night,

we think, would suffer from
extreme conditions.

So Kepler-36b just goes to show
there's so much more

to having a habitable world than
just the composition of the planets.

There's the details of its orbits

and also the nature of the other
objects in the solar system

that are orbiting around the star
with it.

Kepler-36b is just one of
thousands of planets

that Kepler has discovered.

We now know beyond doubt
that our galaxy is home

to a diverse collection of
alien worlds.

Each one of the over 4,000 planets
that we've discovered to date

is different from all the others.

They really are an alien
and exotic bunch,

and there's certainly no planet
that's identical to the planets

that we know of in our Solar System.

And I think that reveals
a deep truth about the universe,

because although the laws of nature
that form the planets are simple

and the same everywhere
and the fundamental ingredients

out of which the planets are made
are simple and the same everywhere,

the nature of a planet also depends
on the history of its formation

and the environment
around its parent star

out of which the planet formed.

And those are all
radically different.

So, each planet has
a different story to tell.

I suppose, in that sense,
planets are like human beings.

And this wholly unexpected
but exciting discovery

certainly complicates
the search for life.

We needed to narrow the search...

..for planets further but not too
far away from their parent stars...

..planets at just the right distance
for their surfaces

potentially to be habitable...

..alien worlds with
one precious ingredient

that makes Earth a living planet.

Now, you might legitimately ask,

"Can we transfer all the knowledge
we have of life here on Earth

"to planets elsewhere
in the universe?"

Well, I would answer emphatically,
yes, we can,

because the laws of nature
are universal.

So, the laws of physics and
chemistry that underpin biology here

on this planet will apply to every
planet out there in the universe,

whether we've discovered it or not.

The chemistry of life requires
a few basic ingredients -

carbon, nitrogen, oxygen, iron.

And it also requires a ready supply
of high-quality energy

from heats within the planets
or perhaps from starlight.

But life here on Earth also requires
one very important, fundamental

extra ingredient,
which is liquid water.

Liquid water is a deceptively
complicated substance.

It's a very powerful solvent,
but it also has structures

which are constantly forming
and disappearing within it,

which act as a kind of scaffolding
around which biology happens.

Organic molecules are orientated
by that scaffolding

so they can react together.

Now, it is certain that
every living thing here on Earth

requires liquid water to survive,

and I would say it is a very good
assumption that every living thing

anywhere out there in the universe
will require it too.

The universe is filled with water.

Great reservoirs have been detected
throughout the galaxy

amongst the gas clouds of
giant nebulae.

But just because water is plentiful,
that doesn't mean that

it necessarily ends up in oceans
on planetary surfaces.

Of the eight planets
in our Solar System,

only one has liquid water flowing
permanently on its surface today...

..an ocean world where, long ago,
life began.

Around 4 billion years ago,
life on Earth would have begun,

probably in places
not dissimilar to this,

where there's geothermal activity,
a source of energy in contact

with rich concentrations of reactive
chemical elements and minerals,

but also, crucially, that -
the magical solvent, liquid water.

Now, many rocky planets out there in
the galaxy will probably have this,

but far fewer, we think,
will have that -

large bodies of liquid water
on the surface.

So that's why there's
a kind of a catchphrase

in the astrobiology community,
which is,

"If you want to search for life,
follow the water."

Whilst life on Earth was evolving...

..124 light-years away...

..amidst a collapsing cloud
of gas, dust and ice...

..a small star was born...

..and the cloud-swirling leftovers
condensed to form a brand-new world.

In 2015, Kepler found a planet

orbiting comfortably within
its star's habitable zone.

More than eight times the mass of
the Earth, K2-18b is a giant...

If the planet is rocky, this may
have allowed it to hang on

to a thick atmosphere.

K2-18b might have all the makings
of a water world.

And a legendary space telescope
had Kepler's new discovery

in its sights.

The most powerful space telescope
of them all had joined the hunt.

Hubble examined the light
from K2-18b's parent star

as the planet passed
in front of it...

..and detected what may be
a faint signature...

..of water vapour.

124 light-years from Earth...

..we may have at last found
the evidence of water

on an alien world.

This was the first observation
of water vapour in the atmosphere

of a planet orbiting in
the habitable zone around its star.

Now, admittedly, measurements
of the amount of water vapour

in the atmosphere is pretty wide.

It's somewhere between 0.01%
and 50%.

I mean, this is a planet
that's a long way away,

but for comparison, our planet has
a few percent water vapour

in its atmosphere.

So, that observation is important
for two reasons.

One is, it is not zero.

There is water vapour
in the atmosphere.

But secondly, if the measurement
is at the lower end,

a few percent of the water vapour
in the atmosphere,

then that is consistent
with this world being a planet

with oceans on its surface.

The nature of this planet
is currently the subject

of intense scientific debate.

The planet may be more like
a mini-Neptune...

..a gas planet.

But it is possible to dream of
a rocky alien world

with skies full of clouds...

..where water droplets collect...

..and eventually fall...

..feeding vast oceans...

..that cover the surface of
a massive planet...

..a water world...

..where the elixir of life...

..is in plentiful supply.

K2-18b is exciting because
it's the smallest world

with an atmosphere that we've been
able to analyse,

and we've found that
its mass and density,

composition of its atmosphere
and its orbits

are consistent with it being
a world with water.

And it might be a world
with oceans on its surface.

We don't know for sure.

But just imagine what
that small, faraway world

around a faint red star
might be like.

Kepler went on to make many
more discoveries...

..until, in October 2018,
it finally ran out of fuel.

After nine years, it had found
over 2,500 alien worlds...

..showing us just how common

potentially Earth-like planets
might be.

We estimate that there may be
around 20 billion

potentially Earth-like worlds -

that's rocky planets in the
habitable zone around a star

that may support liquid water
on the surface - in our galaxy.

That is 20 billion potential homes
for life.

Now, we don't know the probability
that, given the right conditions,

life will begin on a planet, but we
do have evidence from our world.

What we know is that here on Earth,
life began pretty much

as soon as it could after the Earth
had formed and cooled down

and the oceans formed
on its surface.

So that might suggest that whilst
there isn't a sense of inevitability

about the origin of life
given the right conditions,

it might at least be
reasonably probable,

so I think that there is at least
a chance that life may have begun

on some, perhaps many, of those
20 billion Earth-like worlds

out there in our galaxy.

But I think there are
two questions about life.

One question is about the origin
and the existence of microbes.

But often, when we speak about
aliens, what we really mean

is not microbes
but complex creatures.

We need things that we can speak to,
civilisations.

What is the probability there will
be other civilisations out there

in the Milky Way?

Well, again, the answer is
we don't know.

But there are observations
we can make, patterns we can see

in the Milky Way, that might
allow us to make an educated guess.

We don't know precisely

how we highly intelligent,
complex creatures came to be here.

But we do know for certain that
life on Earth didn't begin this way.

We are the product of a story
that has been playing out

for over a quarter of the age
of the universe...

..from microbes...

..to a global technological
civilisation reaching out

for others.

For now, at least, we remain
surrounded by silence.

The messages we've sent out
into the cosmos remain unanswered,

and the telescopes we use to scan
the skies for alien signals

remain quiet.

Now that's not to say, of course,

that there aren't other
civilisations out there.

We may have been looking for
the wrong thing in the wrong place.

But I think the answer to
the question of the great silence

can be found here on Earth,
because, here,

it took 4 billion years of stability
for a civilisation to emerge.

That is a vast amount of time.

And when we look to the other worlds
out there in the Milky Way,

it's those two things -
stability and time -

that appear to be very rare
commodities indeed.

In 2013, the European Space Agency
launched the Gaia Space Telescope.

Its mission? To survey the stars
of our galaxy, the Milky Way.

Billions of stars
have been mapped...

..each star a potential host
for alien worlds.

And patterns are already
beginning to emerge.

Not all stars exist alone.

Some have company.

And bizarre as they seem,

Gaia has discovered around a million
of these binary

or multiple star systems.

We've known for a long time
that binary star systems

and, indeed,
multiple star systems exist,

but we didn't know precisely
how common they are.

But now we have a huge amount
of high-precision data,

including the Gaia data,
which tells us that around 50%

of all sun-like stars
are in multiple star systems.

And for more massive stars,
that number is 80%.

So how does the prevalence of
multiple star systems in the galaxy

shift the odds in the hunt
for another Earth?

Could Earth-like planets
exist in multiple star systems?

And if so, what might their fate be?

In 2020, we may have found a clue,

a planet the size of Mars
floating freely through the galaxy,

a so-called "rogue world".

But planets can't form alone
in interstellar space,

so where did it come from?

Dawn...

..ushered in not by one star...

..but two.

Perhaps the rogue world grew up
in a close binary system...

..subject to the gravitational pull
of two stars.

Its orbit may have been unstable...

..as its parent stars
fought to control its destiny.

Even in single star systems,
the weak gravitational interactions

between the planets
can change their orbits.

Now, in a double star system,

the planets are not only subjected
to the gravitational pulls

of each other, they're subjected
to the stronger gravitational pull

of another star.

So, even if a planet gets into
a stable orbit,

it's very likely that it won't stay
in that orbit for long.

So, in double star systems,
the line between order and chaos

is very thin indeed.

Even subtle changes
in a planet's orbit

can lead to dramatic changes
in climate.

And that's why the surface
conditions on planets

in double star systems may be
unlikely to remain stable enough

for long enough for intelligent life
to evolve.

And the changes in the orbits
of planets

can sometimes be
anything but subtle.

A close encounter may have given
the rogue world

a final gravitational kick.

Flinging it outwards.

And releasing it from the grip
of its parent stars.

Setting it loose...

..on a journey through the galaxy.

Far from the warmth of its stars,

any liquid water the rogue world
might once have had...

..would have frozen solid.

Any atmosphere that once
protected it...

..would have frozen out
on to the surface.

The rogue would have become
a world...

..with conditions that no living
thing could endure.

An entire planet alone and adrift.

Only to be detected by us millions
of years later.

A small Earth-like rogue planet...

..roaming the darkness
of space for eternity.

This lonely wandering planet is not
a unique world.

Although rogue planets are very
difficult to detect,

it's estimated that there may be

over 100 billion of them
in our galaxy.

Rogue planets might be
the most common

type of planet in the Milky Way.

And although we think most of them

were torn away from their star soon
after formation,

this does suggest that star systems
are not always stable places

where complex life could evolve
over billions of years.

Our hunt for another living planet
has only just begun.

Yet we've already learned so much.

We found our first rocky worlds.

Some in the habitable
zone around their stars.

Some, potentially, with liquid
water on the surface.

Candidate worlds for future missions
to search for evidence of life.

But we've also found hordes
of bizarre, tortured worlds...

..orbiting around violent stars.

And a multitude
of rogue planets...

..where complex life as
we understand it seems impossible.

Perhaps it's these worlds
that hint at the reason why...

..for now, one planet stands apart.

Alone.

Our planet seems to have largely
escaped the violence,

the chaos and the constant change

that seems to characterise a galaxy
like the Milky Way.

Yes, there's been the odd
mass extinction,

but there's been an unbroken chain
of life here on Earth

stretching back four billion years.

And if that's what you need to go
from the origin of life

to a civilisation, then although
there may be billions of worlds

out there where life began, there
may be very few civilisations.

But that's just an opinion.

It's an educated guess.

And given the profound nature
of the question,

no matter how educated the guess,
I think it would be ridiculous

for us to stop looking,
both inside our galaxy and beyond.

For we may have just received
the first glimpse

of a world beyond the Milky Way...

..around 30 million
light years away,

nestled in the spiral arms
of the Whirlpool Galaxy.

A world the size of Saturn.

A find that marks an expansion
of our horizons.

The beginning of the hunt
for extragalactic planets.

The potential discovery of a planet
orbiting around a star

in another galaxy is something that
I never thought I'd see.

And it opens up the intriguing
possibility that we might be able

to explore not only the question,
"Are we alone in our galaxy?"

but "Are we alone in the universe?"

The answer to that question may lie
far in the future.

We might never answer that question,

but I said the question
"Are we alone?" is profound

because answering it would teach us
much more

about what it means to be human.

Well, I think we become a little bit
more human with every world

that we explore because that ability
to lay the foundations,

to explore questions to which we may
never receive answers

in our lifetime,
questions for our children

or our grandchildren to answer

is a fundamental part of what it
means to be human.

It's a fundamental part
of what makes us so special

here on this little world,
looking up at the stars,

whether we're alone or not.

Five, four,

three, two...

Engine start. One, zero,

and liftoff of the Delta II rocket
with Kepler

on a search for planets in some
way like our own.

We had worked to get thousands
of people to work together

and it's all coming together.

And we have separation.

It was so emotional to see
the project they had worked on

for so many years or decades
finally go to space

and all that hope and promise all
bundled up in the machinery.

Kepler was an immediate success,

discovering over 2,000 new planets

in its first four years
of operation.

But in the summer of 2012,

the team faced a challenge
that threatened the entire mission.

One of the things that the Kepler
mission needs to operate

are reaction wheels that spin and
hold it on target.

So it always points at the same
stars and doesn't jiggle.

Well, we had four wheels
that did that.

And we knew that we only
had a couple of spare gyroscopes,

and we knew that spacecraft
tend to have gyros fail.

And after a while, it failed.

Three months later,
the second one failed.

And since we needed three,

we could no longer look
at the Kepler field of view.

I had hoped that they'll figure out
a way to work with two gyros,

and indeed they did.

So the very clever people,
the engineers and scientists,

said, "What we can use is we'll use
the sunshine for the third wheel.

"We'll make this thing reflect
sunlight off it,

"we use the other two wheels and now
we can point in the sky."

The faint pressure of sunlight
helped stabilise the telescope.

That was kind of good news,
actually, because it meant Kepler

was going to have to go off
the Kepler field now

and we could get all kinds of other
stars and observe them.

And so, it actually was a boon
for stellar astronomy.

After another four years
of discoveries,

in total it had found
over 2,600 planets,

making it, by far, our most
successful planet hunter to date.

It was sad when they said to command
to shut everything down.

You know, it's asleep now,

it's in orbit around the Sun
and it will continue that orbit,

but since it launched from Earth,
it will come back to Earth.

It'll come and visit us again
in about 40 years.

And my hope is people will say,

"This is a historic telescope.
It told us about all these planets."

And they will go up and pick up this
telescope and bring it back to Earth

and put it in the Air and Space
Museum for us all to admire.

Next time...

..a powerful new space mission
uncovers the history of our galaxy,

the Milky Way.

How it arose from the
universe's mysterious dark age...

..and overcame a series
of enormous collisions

with rival galaxies

that paved the way for our
own arrival

inside one of its magnificent
spiral arms.

Journey through the universe
with the Open University

and learn more about stars, planets
and galaxies with this free poster.

Order your poster by calling
0300 303 5746.

Or go to bbc.co.uk/theuniverse

and follow the links
to the Open University.

I can see everything quite clearly.

It has a stark beauty all its own.

# See me when I float like a dove

# ..The skies are lined
with trees... #

Magnificent desolation.

Beautiful. Beautiful.

Ain't that something?

# ..Come and take me away... #

If I were to ask you,
where do you come from...

..what would you say?

What story would you tell?

You might say, well, I come
from my hometown.

Or my city or my country.

If you've got a particularly
wide perspective, you might say,

"I come from planet Earth."

But what is the largest
structure that we could

legitimately call home?

Well, I would argue it's that.

That faint arc of light
that stretches

across the sky from horizon
to horizon.

It's an outer spiral arm
of our galaxy, the Milky Way.

Our home island of 400 billion
stars.

The Milky Way takes its name
from the dense band of stars

that sweeps across the sky
on the clearest of nights.

From our vantage point here
on Earth,

we see the galaxy from within.

But if we could travel
outside the galaxy...

..we would see the entire structure.

The Milky Way revealed as an island
of light surrounded by darkness.

Hundreds of billions of stars
in a single disc...

..that's existed
since the universe was young.

Only now are we able
to explore its history.

LOW RUMBLING

How it was born.

How, through a series of remarkable
events,

it grew to become the galaxy
we inhabit today.

And how, eventually, it will end.

We've discovered our own paths
in this story, too, living as we do

inside the Milky Way,

just over halfway along one of its
magnificent arms...

..around a small but familiar star.

The Milky Way is an island,
in a sense.

Every star you can see

in the night sky is a part
of our galaxy.

Our nearest neighbour in
large galaxies

is over two million light
years away.

So it certainly feels as if we are
isolated and alone,

adrift in an ocean of dark.

And that is true to a point.

There is no conceivable technology
that will ever allow us

to leave our island physically,

but science allows us to leave
the Milky Way in our imaginations

to view our galaxy from impossible
perspectives in both space and time

and to tell its story.

WOMAN SPEAKS FRENCH

SHE COUNTS DOWN IN FRENCH

Decollage!

One mission more than any other
has deepened our understanding

of the galaxy.

A spacecraft bearing the name
of an ancient Greek goddess.

Everything functioning beautifully.

Gaia.

Coming up on separation of the
boosters.

Ancestral mother of all life
on Earth.

The four boosters, the four points
of light, are falling away.

Gaia's mission?

To map the locations of billions
of stars in the Milky Way...

..nearly all of them
for the first time.

Gaia spins on its axis...

..its sensors scanning the galaxy
in all directions.

Every star is mapped an average
of 70 times...

..allowing Gaia to calculate
the speed and direction of each one,

pinpointing their locations

with accuracies up to
one-thousandth of 1%.

Over 1.5 million stars every hour.

Almost two billion in total so far.

To create a map like nothing
ever seen before.

The Gaia data is by far the most
detailed star map ever produced,

a revolution in our understanding
of the Milky Way.

This is the data,
and it looks like

an artist's impression of a galaxy,
something from science fiction,

but this is a high-precision 3D map
of our home,

of our island of stars,

and we can even fly through it,

such is the precision of the mapping
of the position.

All these points of light are stars,

some of them as far as 30,000 light
years out from the solar system.

The map allows us to journey
through the galaxy

at impossible speeds...

..bringing distant stars
within reach.

But this is also a journey
through time.

The extraordinary thing
about this map is that it's alive,

in a sense. I mean, Gaia didn't
just measure the positions

of these stars.
It measured their velocities.

That means we can tell
where those stars are going,

what the galaxy is going
to be like in the future,

but also we can tell
where they came from.

So what the galaxy was like
in the past.

By reversing the direction
of every star...

..we can rewind their histories...

..travelling backwards in time
through billions of years.

Gaia has initiated a new science,

a science of galactic archaeology,

where we can ask questions
about the origins

of our galaxy itself.

LOW RUMBLING

The first galaxies emerged
just a few hundred million years

after the Big Bang.

The universe was crisscrossed
by a vast structure

known as the cosmic web.

Great filaments of dark matter,

along which gravity attracted ever
denser concentrations of gas...

..separated by immense tracts
of empty space.

The first stars were born
where the filaments crossed,

where the gas was dense enough
to collapse under its own gravity...

..and for the stars to ignite.

New stars formed in their
billions...

..bound together by their mutual
gravitational pull.

These were the first galaxies.

Amongst them, the Milky Way

in its embryonic form,

far smaller and more irregular
in structure

than the mature spiral galaxy
we inhabit today.

The exact details of the Milky Way's
birth remain the subject

of research, but thanks to
modern-day observations, the story

of how our galaxy grew from those
early beginnings

is coming into much sharper relief.

The Gaia data allows us to see
how the Milky Way evolved

throughout its history,

and one of the clues that
it's had an interesting history

can be seen in this animation.

You can see that most of the stars
orbit in very regular orbits

around the centre of the Milky Way -

that's exactly what you'd expect -

but you can see here that
some of the stars

have very different orbits indeed.

They seem to be flying
all over the place.

And that tells us that something
dramatic happened at some point

as our galaxy made its way
through the universe.

Across the universe,

hundreds of billions of galaxies
were forming.

Some, just a few dozen, were born
close enough to the Milky Way...

..that their mutual gravitational
pull drew them together...

..forming what we now know
as the local group of galaxies,

our home archipelago.

DRAMATIC MUSIC PLAYS

Six billion years
before the Earth formed,

some of the Milky Way stars
already had their own planets.

Early worlds that were about
to witness

the transformation
of the galaxy.

The wonderful thing about astronomy
is that you can look

up into the sky, and even if you
can't see worlds,

you can imagine them and you can
imagine their stories.

Over there...

..close to the bright star Vega
is Kepler-444,

the faint ancient star,
and planets orbiting around it,

that's witnessed pretty much
the entire history

of the Milky Way galaxy.

And then maybe
swing around in the sky...

..just close to the planet
constellation

that everybody can recognise

and follow it down.

There's a really faint star there.

You can't see it with the naked eye.

It's so nondescript it doesn't even
have a name. It's got a number.

It's called HD 73394.

But that star is an alien star.

It was born in another galaxy,

and it entered the Milky Way

in a galactic collision
with a smaller galaxy.

And Kepler-444 over there
witnessed it all

and witnessed the Milky Way being
thrown into chaos.

LOW RUMBLING

Kepler-444 was orbited by
five planets.

And something new had appeared
in their skies.

A smaller galaxy
was approaching the Milky Way...

..with stars that burn bright blue.

Gaia Enceladus.

A member of the local group,

roughly a quarter of the size
of our own galaxy.

Over hundreds of millions
of years, the galaxies collided...

DRAMATIC MUSIC PLAYS

..the stars of Gaia Enceladus
penetrating deep

into the Milky Way's heart.

But our galaxy held its ground...

..capturing billions
of incoming stars.

An entire galaxy swallowed whole.

These alien stars remain
in our galaxy to this day.

The Gaia data tell us that
collisions are the driving force

of galactic evolution.

Some galaxies cease to exist
as independent islands of stars...

..while others grow and prosper.

The survival of the fittest
writ large.

When galaxies collide -

that phrase puts images of Hollywood
disaster movies into the mind -

stars getting ripped apart,
but that's not what happens at all.

I mean, if you imagine that
our sun...

..let's say the size of a small
pebble or a grain of sand,

the nearest neighbouring star
in this region of the galaxy

will be somewhere over by
those hills.

The distances between stars
is immense.

The stars don't collide,

so when galaxies interact,
the stars get scattered.

The shape of the galaxy changes,
but nothing gets destroyed.

And in fact,
sometimes galactic collisions

can be engines of creation.

Gaia Enceladus, the alien galaxy,

had brought with it fresh supplies
of interstellar gas.

The raw material of star formation.

For a time, this gas heightened
the rate at which the Milky Way

could produce new stars...

..helping it to grow.

But long before our star was born,

the Gaia Enceladus collision era
drew to a close.

What triggered the formation
of the sun

has long remained a puzzle.

But the Gaia telescope has
discovered

new clues to its origin...

..in the events that followed
billions of years later...

..as our island of stars
continued to evolve.

UPLIFTING MUSIC PLAYS

On the distant shores of
the Milky Way,

Gaia has investigated a structure
of epic proportions.

A stream of stars winding
their way around the galaxy.

This stream of stars is enormous.

It's almost unimaginable in scale.

Look up into the night sky,
those stars that you can see

are at most a few thousand
light years away.

Think about that - the light
began its journey to your eye

from the most distant stars
when the pharaohs ruled Egypt.

And then if you look out
to the Milky Way,

to the shores of our galaxy,

you see light from a few tens of
thousands of light years away.

I mean, that light began its journey
when there were Neanderthals

here in Europe.

But this stream of stars
wraps around the galaxy.

It's hundreds of thousands
of light years in extent.

A structure that large demands
an explanation.

The stream is wreckage,
it's footprints, if you like,

of a very violent event.

Gaia has confirmed the origins
of this immense structure...

..through the telescope's unique
ability to help us

travel through time...

..backwards.

The data tell a story...

..of a new age of star birth.

Of the transformation
of the Milky Way

triggered by another
galactic collision.

It was another galaxy from
our local group.

Sagittarius Dwarf.

Perhaps 20 times smaller
than the Milky Way,

it was torn apart in the impact.

Sagittarius Dwarf brought fresh
supplies of the vital ingredient

for star birth.

HISSING

That is the sound for the most
common element in the universe.

This radio telescope is pointing
towards the Milky Way,

which has just risen
above the horizon over there

behind the clouds.

And what you're listening to
this hydrogen gas.

HISSING CONTINUES

The radio telescope is detecting
the faint signal of hydrogen

from across the galaxy.

Hydrogen is found throughout
the Milky Way,

sometimes in the form of
towering clouds, light years high.

These regions are star factories,

where the dense clouds of hydrogen
gas collapse under gravity...

..to forge new stars.

Hydrogen atoms radiate
radio waves

at a very particular wavelength,
21 centimetres.

And as I speak, that radiation
is being captured

by that radio telescope.

Imagine - there are atoms
over there, and by over there,

I mean, what, thousands, tens of
thousands of light years away.

At some point,
way, way back in the past,

out came the radiation,

and we can listen to it.

So we're listening to the lifeblood
of our galaxy.

As Sagittarius Dwarf passed
through the Milky Way,

it brought fresh gas
AND fresh energy.

The impact sent ripples
across the Milky Way...

..triggering another spectacular
era of star formation.

And in the outer regions
of the galaxy...

..our own star was born.

The sun was soon joined
by the Earth...

..and together,

they set out on their journey
through the galaxy.

We were born in the Milky Way...

..but we may have been conceived in
a collision.

Now, we can't say for certain
that the collision

with Sagittarius Dwarf caused the
formation of our sun.

The date is not precise enough

and our understanding is not deep
enough for that.

But what we can say is that
the birth of the sun coincided

with enhanced rates of
star formation in the Milky Way

caused by that collision.

But that's not quite the end
of the story,

because in a very real sense,
the collision is still under way.

The remains of Sagittarius Dwarf

are still orbiting on the fringes
of the Milky Way.

Over the last five billion years,

the galaxy has crossed our path
two more times...

..each interaction triggering
a new generation of star birth.

A fresh sprinkling of light
inside our galaxy's spiral arms.

The finishing touches on
a masterpiece of galactic creation.

The poet John Donne famously
wrote,

"No man is an island
entire of itself,

"every man is a piece of
the continent, a part of the main,"

by which he meant that no human
being can isolate themselves

from the rest of humanity
because origins and our fates

are so deeply intertwined,

and therefore we must care deeply
for each other.

And the same is true for galaxies.

No galaxy is an island
entire of itself,

and the history
of the Milky Way stretches back

13 billion years or more.

That's pretty much for the entire
history of the universe,

and its story is a story
of collisions and interactions

between galaxies of rivers and flows
and streams of stars

stirring up the void and triggering
the formation of worlds like ours.

You, me, everyone can trace
our origins back

to a collision between galaxies.

You may be small, but you are
a consequence of grand events.

And those grand events
haven't stopped.

It just feels like it because
we don't perceive events

that play out over billions of years
involving billions of stars.

But the unique thing about this time
in history is that we can speak

with some confidence, not only
about our galaxy's past, but also

about our galaxy's future.

And just as inexorably as those
great islands of stars

drift through the universe,
change will come again.

We move into the future with a new
understanding of our place

in the galaxy.

We are inhabitants of a small planet

orbiting around an ordinary star,

where something extraordinary
has happened.

But although the galaxy made us,
it wasn't made FOR us.

We are accidental by-products
of its history.

And we will be passive witnesses
to its ongoing evolution.

The Milky Way is the great survivor,

and the echoes of its turbulent
history are literally

written across the sky.
Over there, in the southwest,

the remnants of Sagittarius Dwarf,
the debris from that collision

is still wandering around somewhere
on the fringes of the Milky Way.

And in that direction, as Sirius
rises in the east

in the constellation of Canis Major,

there are the remains of another
dwarf galaxy

that we think collided with us
long ago.

So the Milky Way pretty much devours
anything that comes into this region

of space because it's the largest
galaxy in the neighbourhood...

..except for one.

The local group is home to another
galaxy that rivals our own in size.

The galaxy that's been hiding
in plain sight.

Right up there,

just between the constellations
of Cassiopeia

and the square of Pegasus,

is a faint misty patch
of light in the sky,

about twice the diameter of a full
moon,

so you can certainly see it
with binoculars.

And even in the city, I can take
a photograph of it

with the camera like this.

And there it is!

That object is the Andromeda Galaxy.

And you see that
it's a spiral shape.

You can see it
even in this photograph.

In many ways, Andromeda is our twin.

And it's a twin that we've been able
to explore in incredible detail.

Three, two, one.

And liftoff of
space shuttle Atlantis

on a final visit to enhance the
vision of Hubble...

..into the deepest grandeur
of our universe.

Standing by for SRB separation.

The Hubble Space Telescope

is in its fourth decade
of operation.

Its ongoing mission has given us
some of the most detailed images

of the universe ever seen.

Over the years, Hubble
has frequently

turned its attention to Andromeda...

..2.5 million light years
from Earth.

It's mapped a spiral structure
similar to that of the Milky Way...

..with such fine precision that
we've been able to calculate

not only the motion of
Andromeda stars,

but also the motion of the galaxy
itself.

And we now know that the entire
galaxy is heading towards us.

That's over
400,000 kilometres per hour.

Now, you may think, well,
what's one more collision?

I mean, the Milky Way has survived
all these collisions

for pretty much the entire history
of the universe.

Well, this one will be different
because Andromeda is bigger than us.

The Milky Way, as we know
it today, will not be immortal.

And the Earth will witness
its demise.

Two galaxies in a single sky,

gradually, but inexorably,
merging into one.

In the impact, there will be a last,
colossal burst of star formation.

But this will be very different
to previous collisions.

This time,

our galaxy will meet its match.

The great galaxies will distort
each of the spiral arms...

..stars will be scattered...

..until no traces of the original
structures remain.

DRAMATIC MUSIC PLAYS

The Milky Way's fate is sealed.

Andromeda will be the first
of a series of mergers

as the remaining galaxies
in our local group converge,

drawn together by gravity.

But Hubble has allowed us to see
even further into the future.

It looks out far beyond the
local group

towards the edge of
the observable universe,

and seeing that every distant galaxy
is receding from us.

In a final twist, these retreating
galaxies tell us something profound

about the nature
of the universe itself.

We live in an expanding universe.

In fact, we live in a universe
that's accelerating

in its expansion, so all
the galaxies are rushing away

from each other, and in the far
future, they'll be rushing away

from each other so fast
that even if we sent a beam of light

out to the galaxies,
it would never catch them.

Billions of years from now,
the remnants of the Milky Way

will form part of a single,
gigantic collection of stars...

..the merged remains
of the local group...

..alone, as every other galaxy
recedes into the distance.

Eventually, all the galaxies
will fade from view,

and our galaxy

will stand at last

in perfect isolation.

An island...

..unto itself.

I think we live at a fortunate time
in the history of the universe

because we can look into the sky
and see the galaxies.

The astronomers of the far future
might imagine that they live

in a universe populated by
countless billions of islands

of billions of stars, but they won't
be able to prove it.

They won't be able to see the true
scale and majesty of the universe.

We've been trying to understand
the band of stars that stretches

across the night sky since the time
of the Ancient Greeks.

This story of our galaxy,
the Milky Way, how it started,

how it was formed

and how it transformed is
really the story of us.

Inside the Milky Way,

you always have a slightly
skewed perspective of the way

the Milky Way looks.

So we're in it.

And so what we would like to do
is go above it and look down

and see what it's like.

Now, you can't do that unless you
could travel at millions of times

the speed of light, and we can't,

so the only way we can do
it is by working out accurately

where all the stars are,

how far away they are from us
in particular.

Gaia is a European Space Agency
spacecraft, which is, in principle,

a very simple little thing.

It's two telescopes collecting
the light, putting it down

onto one giant camera. The biggest
camera ever put in space, actually.

It can observe the positions
of stars so accurately

that you could see the edge of
a euro coin on the moon from Earth.

And that's just mind-boggling.

WOMAN COUNTS DOWN IN FRENCH

Decollage!

It was a beautiful launch,
really spectacular.

Then they got into this critical
state where they had to open up

the sun shields. It was critical
that this opened up

and protect the payload
from the sun,

and that was the do-or-die moment.

There's the good news.

APPLAUSE CONTINUES

Gaia works by measuring parallax.

This is exactly the same way
your eyes and brain work,

so that you can tell how far away
something is

because of the slight difference and
angle from this eye to that eye.

And so what we do with Gaia
is have a picture in the summer

and a picture in the winter,

and in that stage, Gaia has gone
halfway round the sun,

and so its two eyes are twice the
radius of the Earth's orbit apart.

And that's how we do parallax.

All this is a big version
of your head.

The last data released from Gaia
was in December 2020,

and what's been really exciting
is that we've been able to get

the distances and the motions
of the star

to a much better level of accuracy.

Most of the stars in the disc
of the Milky Way

all move in the same direction,

rotating clockwise around the
centre of the galaxy,

and one of the most exciting things
that came out of

the first data release was that
a large sample of stars were found

that seemed to be rotating in the
opposite direction

to the majority of stars
in the Milky Way disc,

and that's really surprising.

They probably came from a different
galaxy altogether,

so there are almost these alien
stars that have been brought in.

Alien stars from galaxies that long
ago shared our own corner

of the universe.

The important thing to know
about our galactic neighbours

is that nothing's actually
sitting still.

We're all moving towards or away
from each other,

and we're sort of playing a dance
out there.

And driving the dance of
the galaxies

is the universe's most elusive
form of matter.

Dark matter is something that
has gravity but produces no light.

It surrounds us.

In fact, it dominates the mass
in our own galaxy,

and yet we don't know what it is.

We can't touch it. We can't feel it.

We were able to start measuring
very accurately the way stars move

from radial velocities, that's just
towards and away from us,

and this allowed us to measure
accurately for the first time

how the dark matter
was distributed near us.

The team have pieced together
how dark matter

orchestrated a series
of galactic collisions...

..that spanned billions of years.

Dark matter is really important
in galaxy collisions

because it's so abundant,

so it's really driving
the gravitational interaction

between the galaxies.

It is dark matter that determines
how violent the collision is,

how rapidly and with what intensity

galaxies come together
when they collide.

In many ways, it determines how
galaxies end up after a collision.

So the thing that Gaia showed us
is not that it's plausible

that this happened,
it showed it DID happen.

It happened in just this way.

So it's not speculation any more.
It's quantitative science.

The galaxy is a dynamic thing.
It's a living organism, if you want.

It is breathing, it is changing,
it is transforming.

It's all coming together in the end
to tell us about how we got here

and what our place
in the universe really is.

Next time - we explore our galaxy's
supermassive black hole.

A monster that can destroy worlds...

..stop time

and is forcing us to reassess our
understanding of reality itself.

Journey through the universe
with the Open University and learn

more about stars, planets
and galaxies with this free poster.

Order your poster by calling
0300 303 5746,

or go to bbc.co.uk/theuniverse

and follow the links to the
Open University.

NEIL ARMSTRONG: I can see
everything quite clearly.

It has a stark beauty all its own.

EXPLOSION

MUSIC: Neptune
by Foals

BUZZ ALDRIN: Magnificent desolation.

Beautiful! Beautiful!
Isn't that something?

The Milky Way seems
a tranquil place.

Hundreds of billions of stars

serenely spinning
through the cosmos.

But journey inwards
through the gas and dust

that shrouds the galactic core...

..and you see a curious sight.

Stars orbiting seemingly
empty space.

Something dark and ancient
lives here.

A hole in the fabric
of the universe.

Every one of those points
of light in the night sky

is a strange and fascinating place.

Magnificent suns with countless
planets orbiting around them.

Alien worlds beyond imagination.

But the strangest and most
fascinating places out there by far

are dark and unseen.

An invisible monster is lurking
in the centre of the Milky Way.

A monster that drains the colour
from the universe.

With the power to destroy worlds.

And stop time.

We've named the monster
Sagittarius A*

and we believe it to be
a black hole.

Sagittarius A* has played
a major role in the evolution

of our galaxy
and may even have influenced

the formation of stars
and planets like ours.

But there is so much more, because
black holes like Sagittarius A*

present the most profound
intellectual challenge.

They are part of nature
just like you and me,

so we should be able
to understand them,

but they are holes in the fabric
of the universe.

They are gravitational prisms
from which even light itself

can't escape.

And in trying to understand them,
physicists have been led

to completely reassess our most
basic understanding of reality.

But there are answers
hiding in the void

for those brave enough to seek them.

EXPLOSION

STEPHEN HAWKING: It is said
that fact is sometimes

stranger than fiction,
and nowhere is that more true

than in the case of black holes.

Black holes are stranger
than anything dreamed up

by science fiction writer,

but they are firmly matters
of science fact.

EILEEN COLLINS: And we copy.
Go for deploy.

You look out and this thing
is so big,

you certainly know that it's moving
over the head of the shuttle.

In the summer of 1999,
Nasa's flagship mission

for X-ray astronomy was released
from the shuttle cargo bay.

There is nothing as beautiful
as Chandra sailing off

on its way to work.

High above the Earth,
Chandra scanned the sky...

..hunting for some of the hottest
regions in the universe.

Exploding stars
and clusters of galaxies.

But on September 14th, 2013,

after 14 years, Chandra chanced
on something else entirely.

The telescope gazed into the
constellation of Sagittarius,

hoping to observe a large cloud
of hot gas.

Instead, it recorded a flash of
X-rays just a few pixels across...

..coming from the apparently
empty space in the galactic core.

Something had got very hot
for a very short period of time.

It's thought that the flash
seen by Chandra

may have been an asteroid
tens of kilometres across.

RUMBLING

Ripped apart and burning up
in a fireball

300 times brighter than the Sun.

The culprit?

Sagittarius A*.

The asteroid's destruction
was our galaxy's black hole

signalling its presence
to the world.

20 years ago, we didn't know for
sure that there is a black hole

at the centre of our galaxy,
but by measuring bursts of radiation

and observing in detail
the orbits of stars

close to the galactic centre,

we now know that Sagittarius A*
definitely exists

and we've been able
to measure its mass.

It is around four million times
the mass of our sun,

which makes it
a supermassive black hole,

one of the strangest and most
powerful objects in the universe.

And we've begun to suspect
that Sagittarius A*

isn't just some strange thing
that sits tens of thousands

of light years from Earth
at the centre of the galaxy.

It has played a crucial role
in the evolution of the Milky Way

and the whole story began with
the death of one massive star.

Soon after the dawn of time...

..the cosmos was home
to colossal stars...

..hundreds of times more massive
than the Sun.

Stars that burned blue
with intense heat.

But the brightest stars
are the shortest lived.

One lived a particularly
fast and furious life...

..burning through its nuclear fuel
in just a few million years.

And with nothing left in the tank,

gravity took over.

The star collapsed...

..ever smaller...

..ever denser...

..until it seemingly disappeared.

The remnants of the star,

now smaller than an atom,

lost from the universe.

All that's left is a ghost.

A black hole.

The genesis of Sagittarius A*
wasn't some bizarre one-off event.

It's possible that almost
all early stars

became black holes when they died.

Black holes are simply what happens
when gravity goes unchecked,

compacting matter so densely

it tears a hole in the universe.

In the vicinity of a black hole,
space and time behave

in very counterintuitive ways.

And in fact, this river
provides a beautiful

and surprisingly accurate analogy.

You see, close to a black hole,
you can think of space itself

as flowing towards the black hole.

Now, here, the flow is not too fast,

and so you could imagine
I could jump into that river,

I can swim faster
than the river of space,

and so I can escape
out into the galaxy.

But as you get closer
to the black hole,

the river of space flows faster
and faster and faster.

A collapsed star is so small
and yet so massive

that close to it, the gravitational
forces become overwhelming.

There is no limit to the speed at
which the river of space can flow.

There's a place where the river
becomes a waterfall,

where no matter how fast I swim,
I could never escape upstream,

and that's what happens
in the vicinity of a black hole.

The river of space flows at and
then faster than the speed of light.

Light itself can't move
fast enough to escape.

And that's what Sagittarius A* is.

It's a waterfall in the fabric
of the universe.

From the moment
the black hole formed,

the seed of Sagittarius A*
had a heart of pure darkness.

The interior forever hidden
from view.

Shielded from the rest of the
universe by a boundary in space.

The event horizon.

The ultimate point of no return.

As we approach the event horizon,

we get our first glimpse of
the true weirdness of black holes.

Einstein taught us that space
and time are not what they seem.

They are merged together
into a kind of a fabric -

- the fabric of the universe.
It's called space time.

And Einstein also taught us that
the presence of massive objects -

stars and planets and galaxies -
curved and distorts

the fabric of the universe.

And that's what we feel
as the force of gravity.

But that distortion is not only
in space, it's also in time.

As you go closer and closer
to a massive object,

the rate that time passes
slows down.

So if I look towards a black hole,

I see time passing slower
and slower and slower

until, on the event horizon,

time stops.

Sagittarius A* was born
a waterfall

in the fabric of the universe...

..where space flows faster
than light

and time grinds to a halt.

But our black hole was still
just a baby...

..dwarfed by the stars around it.

It was nothing like the monster
it would become.

Sagittarius A* today

is four million times the mass
of the Sun.

There has never been a star
that massive.

So it must have formed by the
collapse of something much smaller

and then it must have grown
over the lifetime of the Milky Way

by eating stuff.

Unfortunately, there has been a lot
of stuff around for it to eat.

The young black hole's
inexorable gravitational pull

meant there was no escape for
anything that strayed too close.

Sagittarius A* began to grow...

..pulling on nearby stars...

..before ripping them to shreds
and feasting on the hot plasma.

The black hole gaining more mass...

..and more gravitational power.

But we don't think there were
enough stars nearby

for the black hole to grow
supermassive

on a diet of stars alone.

Instead, it developed a taste
for more massive prey.

When another black hole passed
close to Sagittarius A*,

they became locked
in a gravitational embrace...

..spiralling towards each other,
approaching half the speed of light.

Before colliding.

Sagittarius A* cannibalised
its cousin...

..creating ripples in the fabric
of the universe itself.

More meals were to follow.

Black holes, stars, gas clouds -

whatever ventured too deep
into its lair.

And as our black hole's power
and influence grew...

..its surroundings
were changing, too.

Around the galactic core,

hundreds of billions of stars
were in orbit...

..slowly spinning around
their common centre of mass...

..evolving into the familiar
spiralling disc...

..the majestic Milky Way...

..with Sagittarius A* at its core.

Sagittarius A* became what we now
call a supermassive black hole,

many tens or even hundreds of
thousands of times more massive

than any star in the universe.

And Sagittarius A* is not unique.

We now think that virtually
every large galaxy

has a supermassive black hole
at its heart.

Chandra has looked beyond
the Milky Way

and observed countless supermassive
black holes lurking at the hearts

of the myriad galaxies
that litter the cosmos.

These monsters aren't obscure
quirks of nature.

They are fundamental features of it.

And far from being bit players,

we're starting to realise
that black holes

have the power and reach to sculpt
the galaxies around them.

The centre of our young galaxy
was rich in gas and dust.

More offerings to feast on.

This was a gluttons period

that marks a new era for the Milky
Way's supermassive black hole.

When the invisible monster
became sculptor of the galaxy.

Creation and destruction often
go hand-in-hand in the universe

and black holes are no exception.

Sagittarius A* is certainly not
only an agent of destruction

because the material that falls
inwards towards the black hole

doesn't all vanish
across the event horizon.

A lot of it goes into orbit
around the black hole.

And that region
is tremendously violent.

There are magnetic fields
that swirl around

and become twisted and distorted,
and they can throw material out

along the magnetic poles
of the black hole,

making jets that sweep
through the galaxy.

It's only recently that
we've grasped the true scale

of Sagittarius A*'s eruptions.

Engine start.

One, zero!

Lift off.

The Delta rocket carrying
a gamma-ray telescope

searching for unseen physics
in the stars of the galaxies.

Just over a decade ago, a completely
unexpected discovery was made,

likened to finding a brand-new
continent here on Earth.

The Fermi Space Telescope
was built to detect gamma-rays,

the most energetic radiation
in the universe.

As Fermi orbited the Earth,
it constructed a map of the sky...

..and saw, emerging from the plane
of the Milky Way...

..two colossal bubbles of material,

each 25,000 light years across.

These bubbles are superheated gas.

If our eyes were sensitive
to the wavelengths of light

emitted by those bubbles,
they would span half the sky

as seen from here on Earth.

And they point back
to the centre of the galaxy.

It looks like their origin
is Sagittarius A*.

Think about that.

Sagittarius A* is big
but not big on a galactic scale.

It would fit comfortably
inside the orbit of Mercury

in our solar system.

Though our black hole is only
a fraction of the size

of the galaxy around it...

..it had become sculptor
of the Milky Way.

Every few million years,

the dense ring of material
circling our black hole...

..was accelerated by twisting
magnetic fields...

..into fiery jets
of superheated matter.

Jets so powerful they stripped
the atmospheres

from any planets in their path.

And radiation rendered
every Earth-like world

within a thousand light years
uninhabitable.

But such was the scale of
Sagittarius A*'s outbursts

that far, far out in the galaxy...

..destruction...

..turned to creation.

If you're looking for reasons why
life not only began here on Earth

but was able to prosper for the
almost four billion years it took

for it to evolve into the complex
living world that we see today,

then it might seem
a bit of a stretch

to point to a supermassive black
hole at the centre of our galaxy

and say that's one
of the reasons why.

But we're now beginning to suspect
that those great outpourings

of energy from Sagittarius A*
played a crucial role

in making this region of the galaxy
one in which life can flourish...

..because the hot gas ejected
by Sagittarius A*

had a calming effect on the galaxy.

Now, you might think that a hot
gas cloud would produce more stars,

but, in fact, the opposite is true,

because hot means that everything
is moving around very fast

and that makes it more difficult for
gravity to grab hold of everything

and collapse it to form stars.

So Sagittarius A* reduced
the number of stars

that formed in this region
of the galaxy.

And that's a good thing.

Imagine if there was some giant
star that had formed close by

the exploded in a supernova
explosion.

That would not be a good thing
if you're an amoeba

and you have designs one day
on evolving into Einstein.

So, Sagittarius A* turned what
is potentially a violent region

of our galaxy into a peaceful one.

The warm gases pushed out
by Sagittarius A*

slowed the rate of star formation.

And, around one small yellow star
in a quiet region

at the unfashionable end of the
outer spiral arms of the galaxy...

..four billion years of stability

made all the difference.

Now, of course, there are many
things that are necessary

for life to exist on a planet.

The list is unimaginably vast,
but I think it is interesting

that on that list there is the
presence of this strange object,

a black hole, Sagittarius A*,

tens of thousands
of light years away.

The centre of our galaxy.

Having cleared out much
of the gas, dust and stars

that once lay close by...

..there was little left to feast on.

Our black hole fell silent.

The enormous bubbles
spotted by Fermi...

..echoes of a glorious past.

Today, Sagittarius A*
is a sleeping giant...

..a brooding beast...

..operating on a slow simmer.

Sagittarius A*'s journey
from violent destroyer

to sculptor of the galaxy to the
sleeping giant that we see today

has been pieced together over the
last 20 years by observational data

from telescopes
such as Chandra and Fermi.

But there's a very big
difference indeed

between knowing how a black hole
interacts with its environment,

how it sculpts a galaxy,

and what it actually is
at a deep level.

What is it really like inside?

STEPHEN HAWKING: Black holes
challenge the most basic principle

about the
predictability of the universe

and the certainty of history.

Nothing can get out of a black hole,

or so it was thought.

It's by looking into the future
that we're beginning to explore

the deep mystery of black holes.

Dozens of stars orbit
around Sagittarius A*.

Some passing just a few billion
miles from the event horizon.

A hair's breadth on galactic
scales.

These flybys
could have fatal consequences.

Some of these stars will likely
have planets in orbit.

Planets that may stray too close
to the beast.

A moth to a flame.

Pulled from its parent star
towards the abyss.

If the planet survives its
journey inwards...

..and we could stand on its surface

and look out into the
universe beyond...

..we would see space and time
becoming increasingly distorted.

But eventually, tidal gravitational
forces become too strong.

Inexorably, the singularity awaits.

The end of time,

where all paths terminate.

Over trillions of years,
all the stars around Sagittarius A*

will gradually fade and die.

On more and more alien worlds,
the dawn will fail to come.

But our supermassive monster
will go on,

its secrets sealed away inside.

Seemingly forever.

We predict that one day black holes
will be all that remains

in the universe. The final Dark Age.

BIRD CAWS

If nothing can ever escape
from black holes, if Sagittarius A*

really is an eternal prison,
then this is the end

of the story of the universe.

Darkness littered with holes
in space time.

But we don't think this
is the end of the story.

We now believe that even
black holes die.

And their deaths come at the hands
of what might seem

an inconsequential detail discovered
almost five decades ago.

In 1975, Stephen Hawking
published a remarkable paper

in which he showed that black holes
are not completely black.

They glow faintly.
They have a temperature.

And here's his beautiful equation
for the temperature of a black hole.

And you can see that there's
something deep going on

because this has got all the physics
in it. With this thing here,

h-bar, it's Planck's constant and
that's to do with quantum mechanics,

a subatomic world.
C is the speed of light.

G is the strength of gravity.

This kB here is
Boltzmann's constant,

that's to do with temperature
and thermodynamics.

And this M here is the mass
of the black hole.

It's even got circles
because it's got a Pi in it.

Hawking's conclusion proved
to be irrefutable,

and the implications are huge.

If something has a temperature,
then it radiates.

That's why if you put your hand
near something that's hot,

you can feel it. And so
over timescales that are billions

and billions and billions and
billions of times longer

than the current age of
the universe,

Sagittarius A* will
eventually evaporate away.

Very gradually, the Hawking
radiation

will erode Sagittarius A*.

Smaller and smaller.

Until many trillions and trillions
of years into the future...

..in a final burst of light...

..our black hole will die.

And then there will be darkness.

For all eternity.

Now, you may say,
quite legitimately,

"Well, why do we care?

"Why does it matter if
black holes evaporate away

"some time in the far, far future
of the universe?

"There'll be nobody around to
see it."

But the discovery that black holes
evaporate raises what I think

is the most profound question in the
history of physics, certainly

over the last hundred years,
and that's no exaggeration.

See, what happens if I set
fire to this piece of paper?

With Stephen Hawking's equation
written on it, I cause it

to evaporate away.
Do I destroy everything?

Do I remove every piece
of information, including

the equation from the universe
when it burns away?

Well, the answer is no.

If I could collect every ash,
every molecule of gas that burns off

into the atmosphere, then in
principle I could reconstruct

the piece of paper and everything
it contains.

Every piece of information on
this piece of paper,

including Stephen Hawking's
equation.

But can that be true
for black holes?

The ultimate gravitational prisons?
These objects in the sky

from which even light itself
can't escape?

When they evaporate away,
do they return the information

about everything that ever
fell in back to the universe?

STEPHEN HAWKING: Black holes ain't
as black as they are painted.

They are not the eternal
prisons they were once thought.

Things can get out of a black hole,

both to the outside and possibly
to another universe.

So, if you feel you are in a
black hole, don't give up.

There's a way out.

If information somehow escapes
from Sagittarius A*

as it evaporates away,

the implication is profound.

Black holes aren't tombs.

They're gateways.

We now believe that anything
that falls into Sagittarius A*

will live on.

Not as a physical object,

but as information.

Escaping from the heart of darkness.

Encoded in the Hawking radiation
in the far future.

The memory of all those worlds
that fell into Sagittarius A*

over the entire history
of the Milky Way galaxy is somehow

written in the ashes of the
universe in the far future.

But the real treasure lies
in the explanation

of how the information gets out
from those eternal prisons.

Now, what I'm going to tell you is
going to sound absolutely bizarre.

It's going to sound like science
fiction, but here goes.

When the black hole has evaporated
away, about half of it has gone,

the interior becomes, in some sense,
the same place

as the distant Hawking radiation
that was emitted aeons ago

that's out there in the far reaches
of the universe.

It seems that space time wormholes
open up between the interior

of the black hole and those distant
parts of the universe,

and it's that that allows us to
read the information inside.

Now, that is supposed to sound
weird, and I should say that nobody

really agrees on the physical
picture of what's happening.

But what everybody agrees on is this
- the black holes

are telling us that our intuitive
picture of reality

of space and time is wrong.

The idea that this place
is close to this place

and that time ticks along is wrong.

There is a deeper picture of reality

in which space and time
do not exist.

Our attempt to answer a
seemingly simple question

about the fate of objects that
fall into black holes has led us

to a profound and quite
unsettling conclusion.

Space and time, concepts so
foundational to how we experience

the world, are not fundamental
properties of nature.

They emerge from a deeper reality

in which neither exist.

The thing about black holes

is that nobody
really understands them.

So don't worry if you don't
understand what I'm talking about

because I don't understand
what I'm talking about,

and nobody else does either.

We're still a long way from fully
comprehending the secrets

of black holes...

..but we are beginning
to lift the veil.

Far from being a mere cosmic
aberration,

Sagittarius A* is a part
of our history and of our future.

Our black hole not only
made us who we are today,

it's our teacher,

slowly revealing the deepest
mysteries of the universe.

Secrets sealed away for so long

inside a place beyond forever.

The moral of the story is this.

Understanding the book
of nature is hard,

and so the more of nature
we observe, the more chance we have

of finishing the book.

Now, the strangest objects in nature
by far are black holes,

and so I suppose it's not surprising
that by peering over the horizon

and into the darkness, we have
caught a glimpse of something

deeply hidden - the underlying
structure of reality itself.

So if we want to understand
the meaning of it all,

we can't restrict ourselves
to the intellectually safe confines

of our planet.

We have to look out there
to the universe beyond.

# Baby, you understand me now

# If sometimes you see that I'm mad

# But I'm just a soul
whose intentions are good

# Oh, Lord, please don't let me be
misunderstood... #

So of the seemingly endless zoo
of objects in our universe,

from clouds of gas to planets
to stars, galaxies, what have you,

black holes are probably one
of the most fundamentally important

singular class of objects
that we can study.

A place where the laws of physics
literally break down,

and we have theories, but we can't
really know what's happening.

So black holes present
this remarkable invitation

to physicists, mathematicians,
astronomers.

One of the best tools we have to
study these exotic phenomena

is the Chandra telescope.

Chandra's kind of like a black
hole hunter, finding them

near and far throughout the galaxy
and the universe.

Just a few minutes away from the
26th flight of the Shuttle Columbia

with a crew of five.

I think a night launch
is particularly exciting.

You have a go for start.

We have booster ignition
and liftoff of Columbia.

You just see fire.

It lights up the night sky
in the most beautiful way.

Columbia now has burned
more than 2 million pounds of fuel

and weighs half of what it
did at launch.

It's huge. Chandra is about the size
of a school bus.

It's the largest telescope to ever
be launched by the Space Shuttle.

SRV separation is confirmed.

You're stressed about the astronauts
on board that are literally risking

their lives to help us get
a better view of the universe.

When the main engines cut off, we're
in zero G.

We separate the tank
and we're orbiting the Earth.

And when we're sure that everyone
is ready at mission control

and I go ahead and pull the switch
marked deploy,

and you're looking at the deploy
of the Chandra X-ray Observatory.

Chandra is an X-ray telescope,

which means that it can see the most
energetic light

coming at us from the universe.

The telescope has to be
outside the Earth's atmosphere

because the Earth's atmosphere,

thankfully for us,
blocks out X-rays.

Otherwise, if...
We'd just get fried.

The Chandra satellite, by rising
above the atmosphere,

has a much clearer view.

Why is that so interesting for
studying things like black holes?

Black holes can excite matter
in their vicinity

to very high energies.

They can get atoms and parts
of atoms whipping around

and by revving up those particles
to very, very high energies,

they will radiate

so we can gather enormous amounts
of information

about the immediate vicinity
of a black hole.

When we look at Sagittarius A*
today,

it's quiet and not doing very much.

But when we look at other
supermassive black holes

in the universe, they're active.

So you can take Chandra and watch
a black hole have a small snack,

maybe like a human might have a
little biscuit in the afternoon,

and it's something like an asteroid

and there will be a small sort of
X-ray signature from that event.

But you can also see a black hole
have a really, really big snack,

and Chandra's may be able to witness
that as well.

Chandra has witnessed the
destruction of a star

by a black hole itself, right?

So this poor star wanders
in to the black hole

that it rips the star apart,
it shears it, right?

And then the corpse of that star,

this sort of spaghettified matter
that starts spiralling around

the event horizon lights up
in X-rays.

So to be witness to that, to observe
the destruction of a star,

you know, in time,
was just extraordinary.

It's just unbelievable.

There's this one pretty famous image
that Chandra took called

the Chandra Deep Field South,

and it's the deepest X-ray image
ever.

In that one data set,
there's thousands of black holes,

like maybe 5,000 of them,
if not more.

And it just kind of helps show you
that they're all over the place

and there's so much more
to discover.

Next time...

..we journey back
to the cosmic dark ages,

exploring a time before
the Big Bang...

..to answer the ultimate question.

How did the universe come to be?

Journey through the universe
with the Open University

and learn more about stars, planets
and galaxies with this free poster.

Order your poster by calling...

..or go to...

..and follow the links
to the Open University.

# I'm just a soul whose intentions
are good

# Oh, Lord, please don't let me be
me misunderstood

# Don't let me be misunderstood

# I try so hard, so please,
don't let me be misunderstood... #

Mach 1. Vehicle's now going
supersonic.

Our universe is an enigma.

An endless, inexhaustible paradox.

It's largely...

..a dark, cold and lifeless ocean.

But within this ocean...

..there are islands blazing
with light.

Galaxies.

Trillions of them.

Each one home to hundreds
of billions of stars.

And around many of these stars,
there are planets.

Alien worlds.

Each incomprehensibly strange.

There are trillions of planets
in our universe.

And one of them...

..nurtured beings capable
of contemplating this cosmic drama.

Miraculously improbable.

Brief candles flickering
against the eternal night.

As darkness begins to fall,
if you know that all those points

of light that appear one by one

in the darkening sky are distant
suns,

then it's impossible not
to be overwhelmed at the sheer scale

and majesty of it all.

The universe is infinite
in all directions and

terrifying in all directions.

But if you can overcome your fear,
then questions arise.

And surely the most profound
question of all is, how did all

this come to be here?

That's a question that's defined
much of human history, but it's only

in the last century or so that
we've had the intellectual

and technical tools to interrogate
nature directly, in search

of an answer.

And we've found that it looks for
all the world like there was a first

moment in time, a beginning
to the universe,

13.8 billion years ago -
the Big Bang.

For all the world, but not quite.

Because we've begun to suspect
that there's more to it.

And we've embarked on a heroic quest
to search for and to explore

the time before the dawn.

I can see everything quite
clearly. The light...

It has a stark beauty all its own.

Beautiful, beautiful...

For all the people back on Earth,
the crew of Apollo 8

has a message that we would
like to send to you.

In the beginning, God created the
heaven and the Earth, and the Earth

was without form - and void.

And darkness was upon the face
of the deep.

And God said, "Let there be light".

And there was light.

And God saw the light,

that it was good.

Since we first became conscious
of ourselves...

..we've looked to the heavens,
to those mysterious lights.

Searching for answers.

What is the universe?

How did it come to be?

And what is our place in the cosmos?

We sometimes doubt the creation
stories that our ancestors told.

But those ancient myths
conceal a profound truth.

The clues to the origins
of everything

can be found out there.

In light...

..which ripples to us...

..from beyond the stars.

If we're going to dare to know
about the origin of the universe,

then we have to have some
evidence, and the connection

we have with the deep past is light.

You see, light travels very slowly
on the universal scale, only 186,000

miles a second.

It takes light eight minutes

to journey from the sun to the
Earth.

It takes four years for light
to journey from the next-nearest
star.

And that means we see that star
as it was four years in the past.

So the further out into the universe
we look, the further back

in time we look.

And because we can look way out
into the distant universe,

we can look back towards
the beginning of time.

Go ahead, Charlie.

Well, we have a go for release,
and we're going to be a minute late.

OK, Charlie.

In the quest to find the origin
of the universe...

..we need a time machine.

..Look good,
and we'd like to go

to the next stage.

We concur, Charlie.

A telescope so powerful, that can
peer out so far into the universe

that it can capture the most
ancient light.

Telescope is released.

And carry us back...

..towards the dawn of time.

OK, Charlie.

The Hubble Space Telescope
has taken us on an odyssey

through the universe.

Revealing it's god's...

..and monsters.

Our universe is a place of beauty...

..and terror.

Hubble has shown us visions
of sublime creation...

..and images of awesome destruction.

Illuminating our journey
backwards in time...

..towards the dawn.

The Orion Nebula, a stellar nursery.

Clouds of gas nurturing newborn
stars in the Milky Way.

An image brought to us by light
that left the nebula

1,300 years ago.

The pillars of creation.

Towering, delicate structures,
light years tall.

7,000 years ago.

The Andromeda galaxy.

A glittering island
of a trillion suns...

..two and a half million years
ago.

A cosmic rose.

Galaxies colliding in a celestial
dance.

300 million years ago.

But Hubble's voyage has taken us
even further out into the uncharted

ocean of space.

Glimpsing countless ancient
and faraway galaxies.

Wild and primitive shoals of stars.

Lighting the way to the primordial
past.

Until finally,

Hubble approached the farthest
shore.

A galaxy near the dawn of time.

This is a galaxy called GN-z11,
and it is one of the most distant

galaxies we've ever seen.

This is light from some
of the first stars in the universe.

It began its journey only

400 million years after
the Big Bang.

And it's taken
13.4 billion years to reach us.

When you think about that.

This light journeyed through the
universe,

and after nine billion years
of its journey, the Earth formed.

And then, during the whole history
of our planet, it completed the last

third of its journey,
and entered our telescopes.

So this is an image from the edge
of time.

GN-z11 was one of the very first
galaxies, formed at a time

when the universe itself
was taking shape.

Shortly after the Big Bang.

GN-z11 was a strange galaxy
by today's standards.

25 times smaller than the Milky Way.

But filled with enormous,
violent stars.

Lurking alongside these volatile
giants...

..there were other things.

Delicate objects struggling
in the maelstrom.

Some of the first planets
in the universe.

These were strange, primordial
worlds.

And over the horizon of one of them,

a sun rose.

Marking a new chapter in the history
of the universe.

The beginnings of a relationship
between stars and planets...

..that would,

billions of years later,
on a faraway world...

..lead to the origin of life.

Now, we don't know when or where

the first dawn broke in the
universe.

But what we do know is that

the first dawn was not the first
moment.

The stars and planets
had to come from somewhere.

So the first dawn was preceded
by a long, dark night.

Astronomers call this era
the cosmic Dark Ages.

If we continued to journey
back in time,

we'd see shadows
fall across the universe.

The galaxies would disappear.

The first primitive stars
would be extinguished one by one.

And darkness truly would

be upon the face of the deep.

Here,

in the impenetrable gloom
of the cosmic Dark Ages...

..our quest to understand
the origins of the universe...

..would seem to end.

So how can we peer into the cosmic
Dark Ages to explore the origin

of the universe?

Well, perhaps counterintuitively,
the light from the stars

can still guide us, because that
starlight has been travelling

across the universe for millions
or even billions of years to reach

us, and information about the way
the universe has changed and evolved

becomes imprinted in that starlight.

The stars have illuminated
our voyage through time.

But their light can't guide us
directly across the Dark Ages.

Instead, their light can be used
to build maps of the universe...

..in space and time.

That allow us to navigate...

..towards the moment of creation.

And the most valuable light of
all...

..comes from very particular stars
in the spectacular swansong

of their lives.

Stars exist in a permanent state
of conflict because the force

of gravity is relentless. Left
to its own devices, it will crush

anything and everything,
without limit.

But fortunately, other forces
come into play. As the star

collapses, its core heats
up and turns into a giant

nuclear fusion reactor.

Hydrogen is converted into helium.
That releases energy, which creates

a pressure, which holds the star up.

But stars like our sun burn hundreds
of millions of tonnes of hydrogen

into helium every second.

And although they are big,
they're not infinite in size.

Stars, just like human beings,
have a lifetime.

They are subject to the relentless
march of time.

Now, for stars like our sun,

the collapse continues until it
produces a new and exotic type

of star, known as a white dwarf.

White dwarves are strange beasts.

The fading remains of stars.

Super-dense, planetary-size cores,
usually composed entirely

of carbon and oxygen.

Stars that were once a million times
the size of our planet,

crushed to the size of the Earth.

Subjecting the carbon to extreme
pressures.

And making white dwarves, in effect,

stellar diamonds.

These diamond stars are critically
balanced, able to resist

the relentless inwards pull
of gravity,

but only just.

And that can make them ticking
time bombs.

In 2018, Hubble was in orbit.

The telescope focused on a galaxy
far, far away.

Hunting for a distant white dwarf
that we knew was coming to the end

of its extraordinary life.

For millions of years, the white
dwarf had remained hidden.

Locked in orbit around a much
bigger star.

A red giant.

As they circled each other,

the white dwarf's gravity drew in
gas and plasma from the red giant.

The mass of the white dwarf
increased...

..until it approached,
a critical limit.

Known as the Chandrasekhar mass.

And surpassed it.

Triggering a colossal
thermonuclear reaction.

The white dwarf detonated...

..In a gigantic explosion...

..called a supernova.

That millions of light years away...

..was detected by Hubble.

That white dwarf star or, to be more
precise, the supernova

that it became, has a name.

It's called SN 2018 GV,

and even though it is 70 million

light years away, it is so bright
that we could make a movie on it.

I mean, imagine that - this is a
star the size of a planet

ending its life with a flash
of light that's as bright

as five billion suns.

Now, although supernovas
like these only shine

for a few days,

they cast a profound light
out across the universe.

We've given a name to the sort
of supernova Hubble saw.

They're called type IA supernovae.

And they're common enough to allow
us to map the evolution

of the universe.

Type IA supernovae really
are nature's gift to us.

Because they all explode
in the same way,

that means that they all shine
with the same brightness.

And that means that if we see
one that's dimmer,

it must be farther away.

And that allows us to measure
the distance to the galaxy

that contains the supernova.

And because they shine so brightly,
we can see them tens of billions

of light years away.

That means that we can measure
the distance to galaxies all the way

out towards the edge of
the observable universe.

But there's other information
encoded in the light.

When we look at the light
from distant supernova explosions,

we see something very interesting
and very surprising,

because the light from every
single supernova that's not

in our neighbourhood is redder
than it should be.

And the further away the supernova,
the redder the light. It's called

the redshift.

Now, light has a wavelength.

And the longer the wavelength,
the redder the light.

So the explanation is that
during the time the light

has been travelling from
the supernova to us, space itself

has been stretching, and that's
stretched the light.

And that means that the universe

is expanding.

In our quest to find the origin
of the universe,

this is a vital clue.

Because if the universe
is expanding today,

then tomorrow, everything
will be farther apart.

And it follows that, yesterday...

..everything was closer together.

So if we want to understand
how it all began...

..we have to wind back time...

..through billions of yesterdays.

We have to go back to a time
before the Earth and sun...

..to a time before the galaxies.

And, all the while, the universe
is shrinking.

Getting ever smaller...

..denser and hotter.

Until we arrive at the most
famous moment in the history

of the universe.

Our universe is a place
of infinite variety.

There are galaxies of exquisite
beauty.

Stars of stupendous power.

And planets.

Countless brave new worlds.

Galaxies, stars and planets
are the things that make

our universe remarkable.

They are the things that make
it more than a barren expanse.

How did a universe of light and life
emerge from the cataclysm...

..of the Big Bang?

Unfortunately, we don't know.

We don't even know if the universe
had a beginning.

But we do know a great deal
about how the universe evolved

from a very different state
a long time in the past.

We know that 13.8 billion years ago,
this space that I'm standing in now,

and the space you're standing in
now,

and all the space out to the edge

of the observable universe,
containing two trillion galaxies,

was very hot and very dense
and has been expanding ever since.

Now, that implies that way back,
everything was closer together.

Everything was contained
in a very small speck.

But how small was that speck?

And how did it come to be?

Well, we used to think
that the universe emerged

in that state, very hot and very
dense, at the beginning of time.

And we used to call
that the Big Bang.

But now we strongly suspect
that the universe

existed before that.

And in that sense, it's possible
to speak of a time

before the Big Bang.

So what was the universe
like before the Big Bang?

The first thing to say -

is that it was very strange.

There was no matter.

All that existed

was space-time, and energy,
an ocean of energy.

Almost still.

But gently rippling.

Before the Big Bang, the universe

was a cold, alien, featureless
place.

Picture it as a near-still ocean
of energy, filling the void.

Although it contained no structures,
that energy

did have an effect on space.

It caused it to stretch.

Not the gentle expansion
we see today,

but an unimaginably violent
expansion.

That expansion is known
as inflation.

Think of a speck, a tiny,
insignificant patch of space.

Insignificant, except that many
billions of years later,

this spec would have grown to become
our entire observable universe.

The speck expanded
at a phenomenal rate.

An exponential expansion...

..that lasted...

..for just a few billion, billion,
billion, billionths...

..of a second.

Now, the speck continued to expand
until it was about the size

of this cave, and then inflation
drew rapidly to a close.

And all the energy in that ocean,
that was driving the expansion,

was dumped into space and formed
the ingredients of everything

in our observable universe.

I mean, imagine that - a space
about this size filled with enough

energy to form two trillion
galaxies.

That's what we call the Big Bang.

So the Big Bang was not,
as we commonly imagine,

some kind of explosion.

It was actually a transformation
of energy

into matter.

And the fossilised remains

of these momentous events, the
memory

of the rippling ocean of energy

that drove inflation, became
imprinted

into our universe.

In fact, these fossilised
ripples shaped our universe.

Influencing where each galaxy
and star emerged.

Each planet...

..and moon.

But how do we know all this?

How do we know
that there was a Big Bang?

How do we know that there were
ripples in an ocean of energy

before the Big Bang?

The answer is...

Sept, six, cinq...

..that we've seen them.
..trois, deux...

Planck scanned the entire cosmos...

..looking for light.

Not light from galaxies or stars.

But light from the beginning
of time.

LIQUID DRIPS

This is a photograph of
the distant past.

It's the most ancient light
in the universe.

This is light that's travelled
for almost 13.8 billion years

to reach us.

It's a photograph of the entire
sky, it's like the celestial sphere,

if you like. Every direction
that we can look.

And it's been laid
flat, so we can see it all.

It's called the cosmic microwave
background radiation,

and it's an almost featureless glow.

There are no stars and no
galaxies in this universe.

Now, you might ask the question,
Well, if there are no stars

and there are no galaxies,
then where's the light coming from?

The answer is the light is coming
from the universe itself,

because this is only a few hundred
thousand years after the Big Bang,

so the universe was hot.

So what you're seeing here
is the afterglow of the Big Bang.

The most revealing thing
about this picture

is the detail.

The variation.

This pattern is one of the most
important discoveries

in all of human history,
because it represents one

of the necessary steps in the story
of how we came to be here.

See, that's still ocean of energy
that drove the rapid expansion

of space during inflation,
could not be entirely stellar.

There had to be ripples
in the ocean.

It's a consequence of the laws
of nature, as we understand them.

And those ripples in the ocean
were imprinted into our universe

through the Big Bang, and emerged
as those areas of slightly different

density in the young universe.

And then as the universe continued
to expand and cool, the regions

that were slightly denser
collapsed to form the first

stars and galaxies.

So without those ripples,
we would not exist.

But there's one more extraordinary
thing about these ripples.

And that's the fact
that we predicted them

before we knew they existed.

And then we ventured into space
to test our theory.

Planck's observation of the

afterglow of the Big Bang is strong
evidence

for our outlandish creation saga,

the story of the speck,

the ripples, and inflation.

These ripples, then, are the seeds
of our creation, and we dared

to guess that they exist,

from our vantage point here
on a small planet 13.8 billion years

after the moment of creation.

And then, because we're scientists,

we decided to launch a spacecraft
out into space and capture

the oldest light in the universe.

And we saw that our guess
was correct.

We dared to imagine a time
before the dawn, and we proved

that our creation story
is not a myth.

So here is the creation story...

..as told by science.

In the beginning, there was an ocean
of energy

that drove a rapid expansion
of space, known as inflation.

There were ripples in the ocean.

As inflation ended,

the ocean of energy was converted
into matter...

..by the Big Bang.

And the pattern of the ripples
was imprinted into our universe,

as regions of slightly different
density in the hydrogen and helium

gas that formed shortly
after the Big Bang.

The denser regions of
gas collapsed...

..to form the first stars...

..and the first galaxies.

And nine billion years later...

..a new star formed,

in the Milky Way.

The sun.

The star was joined by eight
planets...

..including...

..Earth.

And nearly 13.8 billion years
after it all began, we emerged...

..blinking, into the light.

in that eternal silence
where it floats, is to see ourselves

as riders on the Earth together,
brothers on that bright loveliness

in the eternal cold.

Brothers who know now
they are truly brothers.

We all have moments of wonder.

We all dream.

Our thoughts float free, soaring
across the Earth and out

into a canopy of stars.

In our most reflective moments,

I think we all understand
that small though we are,

we are connected to the universe.

We are collections of simple atoms.

But atoms arranged remarkably.

With the urge to explore
the universe and to comprehend it.

And celebrate our own place
in this great cosmic saga.

And if we follow that saga back,
it takes us on a pilgrimage.

To a time before the dawn...

..and to strange ripples that
existed

in a universe before our own.

I think we all must wonder
about the meaning of it all.

What does it mean to be human?

Why do we exist?

Why does anything exist at all?

These do not sound like scientific
questions.

They sound like questions
for philosophy, or theology, even.

But I think they are scientific
questions because they're questions

about nature, they're questions
about the universe. And the way

to understand the universe
is to observe it.

I mean, we've seen ripples
in the most ancient light

in the universe, laid down by events
that happened before the Big Bang.

We've seen billions of galaxies
written across the sky in a giant

cosmic web, and we've seen thousands
of planets orbiting around distant

stars, worlds beyond imagination.

Now, the lesson, to me, is clear,

we won't answer the deepest
questions

by being introverted, by looking
inwards.

We will answer them by lifting our
gaze above the horizon and looking

outwards into the universe,

beyond the stars.

We used to look
to the sky and see only questions.

Now, we're beginning to see answers.

Hubble is a very special telescope,
it's kind of like the celebrity

telescope, and for a really
good reason.

It was the first time that we were
able to launch such

a powerful, large optical
telescope into space.

The Earth's atmosphere kind of blurs
out lots of our images.

And so by putting the telescope
in space, we get these precise,

crystal-clear images of our
universe.

Three, two, one and liftoff of the

Space Shuttle Discovery, with the
Hubble Space Telescope.

Our window on the universe.

The feeling that you get
when the space shuttle takes off,

there's just the sort of, the sound
and the vibrations.

It's just incredibly awe-inspiring.

The rocket boosters
have done their job.

Go ahead, Charlie.

We have a go for release, and we're
going to be a minute late.

We were all sort of sitting
on the edge of our seats, waiting

for the very first images
where Hubble is showing us

what it can see in the universe.

And that turned into an unexpectedly
long wait.

Engineers have discovered
that the giant telescope has a

warped mirror, which means the

images sent back to NASA are
distorted.

We had this very, very precisely
engineered mirror, but it

had been very precisely
engineered to the wrong shape.

For the first three years
in the life of the Hubble,

it wasn't producing the wonderful

images that everyone had expected.

The solution was the same solution
to the fact, that as a kid,

I couldn't read the blackboard.

The solution was basically to fit
the telescope with corrective optics

so something analogous
to spectacles.

And we have a go for main engine
start.

..Three, two, one.

And we have liftoff, liftoff
of the Space Shuttle Endeavour,

on an ambitious mission to service
the Hubble Space Telescope.

It's kind of amazing that
we have to be able to position

this optical equipment
to an accuracy of better

than a millimetre, something
that you'd have trouble doing even

on the ground in your bare hands.

Firm handshake with
Mr Hubble's telescope.

Copy that.

The Vice President and I wanted to
call you and congratulate you on one

of the most spectacular space
missions in our history.

And when Hubble opened its eyes
after they were corrected, the views

that we were able to get
from that telescope changed forever

the way we understood and

visualised the universe that we
live in.

CHEERING AND LAUGHTER

The pictures are remarkable.

The trouble with Hubble is over.

It's really hard to remember
what it was like before

we had the Hubble Space Telescope.

We've gotten so used to these
extraordinary photographs

of the near, of the far, of the
very, very far.

I think any time I look at a Hubble
image, my mind gets blown

a little bit.

I was the kid that had, like,
printouts of Hubble images

in their locker.

Anybody, whether they have the heart
of an astronomer or the soul

of a poet, they're going to find
things in the images from Hubble

that just appeal to them
from the point of pure wonder.

Hubble has not only done the things
that people expected and hoped

it would, but it's actually done
a lot of things that nobody

would have dared to dream of.

One of the biggest discoveries
that came from using the Hubble

Space Telescope is that not only
is our universe getting bigger,

it's not just expanding
and stretching, it's actually

getting bigger, faster.

We can well imagine that
the universe is going to continue

to expand and get so big
that eventually the galaxies

will just disappear.

They'll, they'll, be so far away
from us and moving so rapidly,

that we have no hope of seeing
any light from them.

And that's a real possibility
for what could happen in the future.

We still have these mysteries
of what's really driving

this new phase of accelerated
expansion, and we're building

new tools to try to refine
those questions.

The Hubble telescope,
which was a marvel for its time,

is really far behind what we would
design today.

It will be completely outclassed
by the next generation telescope,

the James Webb Space Telescope,
which will see even

deeper than Hubble.

And that will give us unprecedented
detailed views. We can use it to see

through some of the very dense,
murky dust clouds and actually see

stars in the process of forming.

We also can use it to look further
and further back in time.

That's going to be a very,
very exciting story,

which is going to unfold, I think,
within the next three or four years.

Hubble is still king because
it's still a big observatory

in comparison to what we've had in
space before. Hubble is a unique

instrument for making discoveries
that no other telescope

could possibly have made.

I think when you think about
an image of space, when you think

about space, you think of
a Hubble image.

Journey through the universe
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and galaxies, with this free poster.

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0300 303 5746.

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