Brian Cox: Life Of A Universe

I'm on tour in Australia...

Some of them might recollapse in a fraction of a second.

Others might be blown apart by loads of dark energy.

...talking about the life of our universe

to scientists and to space-loving audiences.

I just like having my brain stretched.

I'll probably just stop and have a look at the stars on the way home.

On our journey so far, we've explored how our universe began.

So, this is the oldest light in the universe.

But what about our future?

Is there an end of the universe? Is our universe eternal?

The universe literally tears itself apart.

There is some true vacuum somewhere.

We could tunnel into it at any moment.

Does it make any sense to talk about this universe

in 100 billion, 200 billion, a trillion years' time?

Will there be stars and galaxies?

And people, and questions,

and astronomers, and televisions?

What IS the fate of the universe? How will it all end?

I suppose we all get used to the idea that we live finite lives,

and perhaps that's 'cause we imagine we can leave a legacy -

our children and grandchildren, great works.

But will that legacy be eternal?

Can we imagine taking the great achievements of our civilisation

and chiselling them into granite and leaving them

as a record into the far future?

Or do the laws of nature conspire to make that impossible?

Will all trace of our civilisation one day vanish?

What will be our fate?

And what is the ultimate fate of the universe?

I'm going to investigate the theories that cosmologists have put forward

for the end of days.

There is a law of physics

called the second law of thermodynamics,

and to paraphrase it, it means that on a global scale -

so, across the universe -

things can only get worse.

So, things tend to get more disordered,

things tend to decay away.

I was once involved in putting forward the opposite proposition -

things can only get better -

but that is a gross violation of the second law of thermodynamics.

It really shouldn't have been allowed even in a song lyric.

I think, actually,

songwriters should pay more attention to fundamental physics.

The first stars in our universe began to shine

around 100 million years after the big bang.

But it was another 9 billion years before our star, the sun, formed.

But our sun won't live forever,

which will obviously have a direct impact on all life on Earth.

The sun is about halfway through the phase where it's burning hydrogen.

It's making helium.

It's got what we call the 'solar luminosity' -

it's putting out that much heat and light.

But that is going to be slowly increasing.

Presumably at some point we would find it extremely uncomfortable here.

Yeah.

In about 1.1 billion years,

it will have got to 10% brighter than it is now.

That is enough to create what's called a moist greenhouse.

So life on Earth will become very problematic at that stage.

3.5 billion years from now,

it'll be 1.4 times its current luminosity,

and that's enough to evaporate the oceans.

Right.

So that's getting fairly severe at that stage.

It's really got another 5 billion years to go

that it can keep on burning hydrogen,

but it will become uncomfortable for us well before that.

The destiny of stars like our sun is to run out of fuel and collapse.

The core compresses, but the rest of the star expands enormously

and we have a red giant.

So we enter this red giant phase.

When our sun becomes a red giant

and it begins to swell and engulf the orbit of Mercury,

it's gonna start getting very hot on Earth.

We're gonna need ways to terraform Mars

and then ship billions of people to Mars,

because Mars will be cooler than Earth,

it being one and a half times farther away.

The Earth will basically get fried at that point.

We won't be able to exist.

Hopefully, if humans are still around in some form or another,

we've moved off to better locales.

So, the ultimate fate of our star, the sun, is to be this cooling ember?

That's the ultimate fate of the sun.

So, in just over a billion years, this place will become uninhabitable.

In 6 to 7 billion years, the sun will be gone.

But that, of course, isn't the end for the universe,

and matter that floats out from our dying sun

will recollapse to other stars, other planets

and perhaps other living things.

But that process can't go on forever.

There comes a point in the life of the universe

when the constant recycling, the births of new stars, has to stop.

So, what IS the fate of the universe?

How will it all end?

Cosmologists have thought about this for a long time,

and many have come to the conclusion that the end will come

in more of a whimper than a bang.

It's known as the heat death,

and it begins with a decrease in the rate of star formation.

Looking up into the southern sky

allows us to see a hint of this process.

As soon as you look through a telescope,

you do get a sense of the amount of gas and stuff out there, don't you?

You always hear this wonderful phrase 'stellar nurseries'.

So, is that really accurate,

that you really do have these places where all the action is concentrated?

Absolutely.

In order to form stars, you have to put together a lot of material,

and so you naturally pop off a lot of stars in that particular area.

I can't... I can't stop looking, actually.

Fortunately, we have very powerful telescopes

to see all the way across the galaxy

so that we can pick out stars

in all kinds of stages of their formation process,

from when they just start collapsing

to when they really kick on and turn into full-blown stars.

Stars form from collapsing clouds of gas and dust.

And the leftover material forms into planets and moons

and asteroids and comets.

But in our part of the Milky Way,

this construction process is slowing down.

Is this a glimpse of the beginning of the end?

We see that around the, sort of, solar neighbourhood,

around where the sun lives,

that there's about half as much star formation

as there was 10 billion years ago.

Why is that?

Once you form a star, it dies

and it holds some of its matter together

in a black hole or a white dwarf or a neutron star,

and you've locked that gas up forever

and it never goes back to being a star again.

So in order to keep forming stars,

you've got to keep bringing gas in from somewhere else.

So the fact that the rate is dropping...

...you said a factor of two from, what, 10 billion years ago to now,

implies, of course, that some time in the future, that's gonna stop.

So, when is that?

It's a long time. Not in our lifetimes.

I think if you do the extrapolation,

you go out 100 billion years or something, more than that.

It's a long time away.

Eventually, we will run out of gas to form new stars

in every single galaxy,

and gradually, gradually, gradually, the universe will... die away.

So, what will our descendants actually see

when they look up into the night sky in a few billion years' time?

Well, the centre of the galaxy is here, isn't it?

Yeah. It's kind of the empty bit of sky up here - Sagittarius.

Peer into the centre of the Milky Way

and, like virtually all other galaxies,

you'll find a supermassive black hole.

Ours is around 4 million times the mass of the sun.

We don't know how these supermassive black holes form,

but we do know about smaller, stellar-mass black holes.

And when the centre of those stars are more massive

than about two or three times the mass of our sun,

they actually collapse into a singularity,

is the theory,

and the space-time around them bends completely on itself,

so nothing...

The gravitational pull is so strong, nothing, even light, can't escape.

So, then we're left, I suppose, with a dark sky,

but a sky full of black holes...

Yeah. ..and, what, fading stellar remnants?

Yeah, fading stellar remnants.

Things like faintly glowing cores of long dead stars,

billions or even trillions of years in the future,

and these are glowing so faintly, you can't even see them.

Now, black holes do radiate very, very faintly,

but we won't actually be able to see that,

because they'll all be too far apart.

You get the sense, I suppose, when you talk about that,

this starry sky, we take for granted.

Although, perhaps we don't.

You know, perhaps it's the most beautiful thing

but it's a temporary phenomenon.

It's actually a very short-term phenomenon, isn't it?

We're only nearly 14 billion years into the universe's history.

So in the far, far future, hundreds of billions of years' time,

if we could still stand somewhere and look out into the night sky,

we would see just blackness,

and there would be no hints at all to tell us

about the past glorious history of our universe.

But is this the whole picture?

Science has a habit of opening up new possibilities -

often when you least expect them.

We've known our universe is expanding since the 1920s,

and we thought the expansion rate was slowing down.

Then, in the late 1990s, it was discovered

that the expansion rate of our universe is actually speeding up.

Nobel Prize winner Brian Schmidt

was as surprised as anyone by his discovery.

1998, we went through and we measured

that the universe wasn't slowing down at all - it was speeding up.

And that was... well, it looked to me like a big mistake