All language subtitles for BBC The Beginning and End of the Universe

It is a good rule of thumb
that, in science,

the simplest questions are
often the hardest to answer.

Questions like,
how did the universe begin?

In fact, until relatively recently,
science simply didn't have the tools

to begin to answer questions
about the origins of the universe.

But in the last 100 years,
a series of breakthroughs have been

made by men and women who,
through observation, determination

and even sheer good luck, were able
to solve this epic cosmic mystery.

This was real astronomical gold.

I am going to recreate
their most famous discoveries

and perform
their greatest experiments...

30,000 km/s.

..that take us from the very biggest
objects in the universe

to the infinitesimally small,

until I reach the limits
of our knowledge by travelling

back in time to recreate
the beginning of the universe.

The moment one millionth of a second
after the universe

sprang into existence.

This is a time before matter
itself has formed in any way

that we would recognise it.

It is as close as we can hope
to get to creation,

to the beginning of time,

the beginning
of the universe itself.

It is a remarkable fact that science
took hundreds of years to come up

with a theory to explain
the origins of the universe.

All the more surprising,
given what a simple

and fundamental question it is.

There is something quintessentially
human about asking the question,

where does all of this come from?

Perhaps because it is a deeper,
more fundamental version of

where I come from?

Yet, for most of human history,
the answers to such an apparently

simple question could only be
attempted by religion.

It wasn't until the middle
of the 20th century that science

built a coherent and persuasive
creation story of its own.

It was a story based on theory,
predictions and observation,

a story that could finally explain
what had happened at the very

beginning of time, the beginning
of the universe itself.

A little over 100 years ago,
if scientists considered the life of

the universe at all, they considered
it eternal, infinite and stable.

No beginning and no end.

So even framing the question
about the origins of the universe

was impossible.

But at the beginning of the
20th century, that began to change.

New discoveries shook
the old certainties

and paved the way for questions
about where the universe came from.

One observation transformed
our idea about

the true scale of the universe.

It began with a mystery in the sky.

By the early part of the
20th century, it was well known

that our solar system way
within a galaxy, the Milky Way.

Every single star we can
see in the sky with the naked eye

is within our own galaxy and,
until the 1920s, all these stars,

this single galaxy, was the full
extent of the entire universe.

Beyond it was just an empty void.

But there were some enigmatic
objects up there as well,

just discernible to the naked eye
that looked different.

And one of the most
notable is Andromeda.

You can find Andromeda
if you know where to look.

So, if you start from Cassiopeia,
those five stars

shaped like a sideways letter M,
if you move across from the point,

from the points of the M, slightly
up is where you should find it.

Now, I'm going to use my binoculars
to help me in the first instance.

And if I zoom across...

Yeah, there it is.

You can tell it's not a star.
I mean, it's basically

a very faint smudge stuck
between those two stars.

That is it straight up there -

that is M31,
the great Andromeda nebula.

Now, they were called nebulae,
because they had this smudgy,

sort of wispy, cloudy nature.

In fact, the word nebula
derives from the Latin for cloud.

These indistinct objects were found
scattered throughout the night sky.

Telescopes revealed many of these
nebulae were far more complex

than simple clouds
of interstellar gas.

They appeared to be
vast collections of stars

and that raised
two intriguing possibilities.

Were these stellar nurseries
places where stars were born,

and therefore residing
within our own galaxy, or,

much more profoundly, were these
beautiful, enigmatic objects

galaxies in their own right
sitting way outside the Milky Way?

The implications of that
second possibility were enormous.

If true, it would instantly

and utterly transform our idea
about the size of the universe.

Here was an opportunity
for an ambitious astronomer to make

a real name for themselves.

Perhaps someone with
a really big telescope.

Step forward this man -
Edwin Hubble, a man from Missouri,

although if you had ever met him,
you'd never have guessed,

because he developed this weird
persona, a pipe smoking tea drinker

with a very affected
aristocratic English accent.

Hubble is probably the most
famous astronomer ever,

not least because of his consummate
skill at self-promotion,

but also because of the incredible
measurements he would make.

In Hubble's day,
when it came to observations

and new discoveries, size mattered.

Today, this is the most powerful
optical telescope in the world,

the GTC, with a primary mirror

over 10 metres,
or 400 inches, in diameter.

Far bigger than anything Hubble had.

In September 1923,

Hubble was working at what
was then the biggest telescope

in the world,
the 100-inch Hooker telescope

at the Mount Wilson Observatory,
perched on top of the

High Sierra mountains overlooking
Los Angeles in California.

He was using the telescope
to study one of the most prominent

nebulae in the sky,
the Andromeda nebula.

The same nebula I looked at earlier,
and it was while observing it

that one very special star caught
Hubble's attention,

one that could reveal
the true nature of Andromeda.

And I am going to use this
telescope to look for it now.

This is the control room of the GTC
and, tonight, they've pointed

the telescope at Andromeda and they
are going to take a picture of it.

It takes about a minute
for the exposure

to give you a clear enough image?
That's right.

Now, the picture is finished,
so we're going to open it.

OK, so, this is Andromeda here.

That's Andromeda, that's right.

And now,
this is Hubble's original plate.

Right, now, Hubble's star
is down here in this corner.

Can you find it in your image?

Yeah, if you take the image
and you compare it,

you will see that
we don't see that one.

What we see is the edge
of the galaxy,

so we have to go
a little bit further west...

Oh, I see, so all this is just
the edge. That's the edge.

I was assuming it was the centre
of the galaxy. No, no, no.

It just goes to show how much more
resolution your telescope can get.

That's right. OK, so,
can we see that particular star?

Yes, in order to find
that particular star,

because it is so faint,

we have to look for references
which are brighter.

And, in this case,
you will see four stars in here,

which are these four stars.

And the star Hubble found
will be this one here. That's it...

That tiny star is the one
that Hubble found.

That's amazing.

And are you able to get
a magnitude for that star?

Yeah, we have to do a little
bit of processing on the image,

but we are able to get it.

OK. Hubble had found his star.

He knew it was special,

because he compared his plate with
others taken over previous nights

and he noticed that his star
changed in brightness -

some nights it was brighter,
some nights it was dimmer.

He realised this is a variable star,
and he saw the significance of it.

He could see that this was real
astronomical gold.

His star was a Cepheid variable.

In the stellar bestiary,

Cepheid variable stars hold
very special place...

..because, by studying
the way their brightness changes,

astronomers can calculate
how far away they are.

Hubble's Cepheid was the first
to be discovered in a nebula,

so he knew that,
if he could measure its period,

he would be able to work out
its distance from us.

So, Hubble set about
meticulously measuring

how his star's luminosity varied.

It's not hard to imagine
how exciting

this must have been for Hubble.

At his fingertips was
the opportunity to resolve

a fundamental yet simple question -

was this nebula within
the Milky Way or beyond it?

The answer would reshape
our knowledge of the universe.

Hubble measured the luminosity,
or brightness,

of his star over many nights
and plotted this curve here.

Now, when we measured tonight,
we found it had a value of 18.6

and I know because they measured
it last night to be slightly dimmer

that it falls
on this side of the curve.

But more important is the period,

the time in days, from peak
brightness to peak brightness.

Hubble measured this
to be 31.415 days.

This is the critical measurement.

Armed with this
and its apparent brightness,

Hubble calculated the distance
to the Andromeda nebula.

It was immediately apparent
that this star is very far away.

But when Hubble did his calculation,
he worked out that it was

900,000 light years away,

making this star the most
remote object ever recorded.

It could mean only one thing -

not only is Andromeda
a galaxy in its own right...

..but it lies well beyond
our own Milky Way...

..and the myriad of other elliptical

and spiral nebulae were also
individual distant galaxies.

It was a moment in human
consciousness when the universe

had suddenly and dramatically
got considerably bigger.

With this observation, Hubble had
redrawn the observable universe.

It might not have directly
challenged

the idea of a stable universe,

but it shattered long-held
assumptions and opened

the possibility
of other bigger secrets,

like an origin to the universe.

Into this profoundly-expanded cosmos
strode someone who would,

without realising it, provide
the tools to unlock that secret.

This guy.

A story as great as one
that explains

the origins of the universe would
somehow feel wrong without involving

a scientist as great
as Albert Einstein.

And so, of course, it does,

because it was Einstein who provided
the theoretical foundations

needed to study the universe

and effectively invent
the science of cosmology.

100 years ago, he proposed his
general theory of relativity.

It turned physics on its head
and gave us

a completely new understanding
of the world.

He proposed that gravity was
caused by the warping

or bending of space-time by massive
objects like planets and stars.

His theories were revolutionary.

Einstein was a maverick who ignored
the conventional

to follow his own remarkable
instincts.

One of his lecturers once told him,

"You are a smart boy, Einstein,
a very smart boy.

"But you have one great fault -

"you do not allow yourself
to be told anything."

Of course, it was this very quality
that would allow him

to change the world of physics
and, of course, to mark him out

as one of the greatest thinkers
of the 20th century.

And in 1917, he took
his general theory of relativity

and applied it
to the entire universe.

By following the logic
of his theory,

he arrived at something
rather unsettling -

the combined
attraction of gravity from all

the matter in the universe
would pull every

object in the cosmos together,
beginning slowly

but gradually accelerating until...

Gravity would ultimately

and inevitably lead to the
collapse of the universe itself.

But Einstein believed,
like virtually everyone else,

that the universe was eternal
and static and certainly wasn't

unstable or ever likely
to collapse in on itself.

But his equations appeared
to show the opposite.

In order to prevent
the demise of the universe

and keep everything in balance,
he adds this in his equation -

Lambda,
or the Cosmological Constant.

It is a sort of made-up force
of anti-gravity

that acts against normal
gravity itself.

Now, he had no evidence for this,
but it helped ensure

that his equations described
a stable universe.

Within his grasp was the secret
to the origins of the universe.

Yet Einstein simply couldn't,
or wouldn't, bring himself

to accept the implications
of his own equations.

With hindsight, it seems remarkable
that Einstein did this.

I mean, here was a man
who had revolutionised science

by rejecting conventional wisdom

and yet, he couldn't bring himself
to trust his own theory.

He felt compelled
to massage his equation

to fit the established view.

He even admitted that
the Cosmological Constant

was necessary only for the purposes
of making a quasi-static

distribution of matter, basically
to keep things the way they were.

Whatever his reasons,
this little character, Lambda,

would return to haunt him.

Because, while it prevented
Einstein from understanding

the implications...

..his ideas opened the way
for someone else to propose

a theory for the origin
of the universe.

He was a young part-time university
lecturer of theoretical physics.

His idea was so radical,
it shocked the world of physics

and split the scientific community.

He started an argument that wouldn't
be resolved for half a century.

His name was Georges Lemaitre.

Now, the eagle-eyed might spot
the dog collar.

In fact, he was both a physicist
and an ordained priest.

Of this apparently curious
dual role,

Lemaitre said, "There were
two ways of pursuing the truth.

"I decided to follow both."

And, using Einstein's
theory of relativity,

he developed his own
cosmological models.

Lemaitre's model described
a universe that,

far from being static,
was actually expanding,

with galaxies hurtling away
from one another.

Furthermore, Lemaitre
saw the implications of this.

Winding back time, he deduced
that there had to be a moment

when the entire universe
was squeezed into a tiny volume,

something he dubbed
the primeval atom.

This was essentially the first
description of what became known

as the big bang theory, the moment
of creation of the universe.

These were revolutionary ideas
and so he published them

in the Annales de la Societe
Scientifique de Bruxelles,

where they were promptly ignored
by the scientific community.

So, he travelled to Brussels to try
to gain support for his idea.

The 1927 Solvay Conference,
held here in Brussels, was probably

the most famous and greatest
meeting of minds ever assembled.

But for our story,

the most significant meeting
didn't happen here.

It wasn't planned and happened
away from the conference.

It happened here.

In this park, the unknown Lemaitre
approached the most famous,

the most feted scientist
in the world -

Albert Einstein.

Here, finally, was his chance to
explain his idea about an expanding

universe to the very person whose
theory he had used to derive it.

You can only imagine Lemaitre's
trepidation as he approached.

If Einstein
endorsed his radical idea,

then surely it would be accepted.

Surely this brilliant mind,
this titan of physics,

this deeply original thinker, would
see the merits of his theory.

But after a brief discussion,

Einstein rejected his idea
out of hand.

According to Lemaitre, he said,

"Vos calculs sont corrects,

"mais votre physique
est abominable."

As far as Einstein was concerned,

his maths might have been correct,
but his understanding

of how the real world worked was,
well, abominable.

Once again, Einstein dismissed
the idea of a dynamic universe.

Lemaitre's paper should have
ignited science,

but without the backing of such
a huge and influential figure as

Einstein, his ground-breaking idea
was doomed to be quietly forgotten,

unless some observation or evidence
showed up to support

the idea of an expanding universe.

Edwin Hubble, here, was riding high
after his discovery that

proved there were galaxies
outside of our own.

He was feted by
Hollywood glitterati,

a guest of honour at the Oscars,

and, with access to the world's
most powerful telescope,

he was ready for his next challenge.

He had heard of some unusual
observations that many galaxies

appeared to be moving away from us.

No-one could understand why
this might be.

So, in 1928,
the world's most famous astronomer

turned his attention to this new
cosmic mystery and began to measure

the speed that these galaxies
were moving relative to Earth.

To measure the velocity that
a galaxy was receding from us,

Hubble use something
called redshift.

Now, it's not a perfect analogy,
but the effect is similar to one

most of us are familiar with
in sound -

the pitch of a car engine
as it approaches us is higher,

because the sound waves
are compressed,

but the pitch drops lower
as the car recedes,

because the sound waves
are stretched.

The effect is similar
with light waves.

As the source of light moves
towards us, the observed wavelength

is squashed towards the violet
or blue end of the spectrum.

But if the source is
moving away from us,

the wavelength is stretched towards
the red end of the spectrum,

or redshifted,
in the parlance of astronomers.

And the greater the velocity
the object is receding,

the greater the redshift.

With his assistant, Milton Humason,
Hubble spent the next year

carefully measuring
the redshift of galaxies.

And I have got the chance to do
the same thing right now

using this telescope.

OK, Massimo,
have you found a galaxy for me?

Yes, I found this galaxy.

So, how far away is this?

It is approximately
430 megaparsec far.

So, if you convert that to
light years... 430 x 3.26...

So it's about
1.5 billion light years away.

Yeah, yeah. OK.

Hubble needed to measure the average
light coming from the galaxy

in order to get a spectrum, so that
he could calculate the redshift.

Now, Humason did this by exposing
a photographic plate

and it took him a whole week
to collect enough light

to get the spectrum.

But here at the TNG, the Galileo
Telescope, they use instead

a very sensitive chip that
can do this much more quickly.

How long does it take for you
to get a spectrum?

Approximately 10, 15 minutes.

So, 10 or 15 minutes' exposure
compared with a week

back in Hubble's time -

far more powerful than anything
they had back then.

It's done.
The spectrum is quite good.

Ah.

OK, so this is the raw spectrum
that has been taken.

Is there a particular
emission line here that you will

use as your reference
to measure the redshift? Yeah.

Here, for example,
you have an emission line,

but to obtain real spectra,

you have to clean it
to obtain the final one.

Ah, this is the cleaned-up
version of that. Yes, of that.

So this is the actual emission lines
from the galaxy... Yes.

And this one below, I guess,
is the reference?

The reference, correct,

of a galaxy with redshift zero.

OK, so one that isn't moving away
relative to us. Yes.

And so it is very clear here, if you
compare the top one with this one,

every emission peak is shifted.

It's shifted in the red.

The reference line for
the sample is H-Alpha,

and, from these, you can compute
the redshift of this galaxy.

And can you work out
from that how fast

the galaxy is moving away from us?

In principle, you can obtain this.

OK, so what is the formula?

The formula is the difference
between the reference wavelength

and the observed wavelength,

divided by the reference wavelength
and multiplied by C.

This is the Doppler effect.

Let's see if we can do that roughly.
Yes.

OK, so this is about...

7,200, approximate.

OK.

Minus 6,563.

..63. OK. Over...

6,563.

And that is the fraction
of the speed of light? Yes.

OK, so, I might as well do this.

I should do it with
my calculator, but...

So...

OK.
So then that we divide by 6,563.

OK, so it is roughly
0.1 the speed of light.

So it is about 30,000 km/s, yes?

Correct. Thank you.

OK.

I'm actually quite pleased
at my maths here,

because I was under pressure.

So, this galaxy is 1.5 billion
light years away from the Milky Way

and, from the redshift,

we have worked out it is
moving away from us

at 1/10 the speed of light.

That means it is moving away
from us at three...

At, sorry, 30,000 km/s.

Boom.

Science.

Once he had calculated
the speed of the galaxy,

Hubble then measured
how far away it was.

Once Hubble had
both his measurements,

he could start putting them on a
graph of velocity against distance.

Now, he made 46 different
measurements

and, when he put them on the graph,
he noticed a pattern emerging.

He could draw a line through
all these points -

each one of them
is an individual galaxy.

He noticed a connection
between the velocity

and the distance of a galaxy.

In fact, the further away it was,

the faster it was
moving away from us.

In a stable universe, the speeds
of galaxies should appear random.

You wouldn't expect
a clear relationship

between the distance
of a galaxy and its velocity.

Hubble's graph showed that
the universe was expanding,

which has profound implications
for the idea

of a beginning to the universe.

What this means is that it is not
just that the galaxies

are all speeding away from us
and from each other

but that, if you could
wind the clock back,

there would have been a time when
they were all squeezed together

in the same place.

Here, finally,
was the first observation,

the first piece of evidence that
Lemaitre's idea of a moment

of creation, of a universe evolving
from a Big Bang,

might be correct.

Thanks to Hubble's work,
Georges Lemaitre,

the unknown Belgian cleric,

the theoretician without proper
international credentials,

the man whose physics Einstein
called abominable,

was belatedly rightly recognised
for his bold theory.

Most significantly,

the biggest name in physics came
around to this revolutionary idea.

In 1931, on a visit
to Hubble's observatory,

Einstein publicly endorsed the
Big Bang expanding universe model.

"The redshifts of distant nebulae

"has smashed my old construction
like a hammer blow," he said.

Einstein dropped the cosmological
constant. He even wrote to Lemaitre,

"Ever since I introduced the term,
I have had a bad conscience.

"I am unable to believe
that such an ugly thing

"should be realised in nature."

It must have been quite
an absolution for Lemaitre.

Having been practically cast out
into the scientific wilderness,

he was now firmly at the centre
of a cosmological revolution.

The idea of the Big Bang
was finally gaining traction.

But, despite Einstein's
seal of approval,

and the observations of Hubble,

the argument was far from over.

There were still significant
objections

if the idea of a Big Bang
was to be widely accepted.

A scientific theory of creation
isn't just about explaining

the expansion of the universe -

there were more profound
issues to resolve.

The problem was, the Big Bang raised
as many questions as it answered.

Like, if the universe had
erupted from a single point,

where did all the matter come from?

To go further, the Big Bang theory
needed to explain

how matter itself had been formed.

Well, before that could be answered,
we need to know

what the universe is actually made
of - the elemental building blocks.

And working that out took
an incredible bit of insight

by a remarkable woman -
Cecilia Payne.

She studied at Cambridge University,
but wasn't awarded a degree,

because, well, she was a woman.

So, to continue to her studies,

she needed to go somewhere
more enlightened.

She left England for America

and it was there that she revealed
the composition of the universe.

If you were to ask someone
what the most common elements were,

an atmospheric scientist
might say nitrogen.

After all, it makes up more than
three quarters of the atmosphere.

A geologist might say silicon
or iron or oxygen...

which all seems very quaint
and Earth-centric

and really rather parochial.

So, astronomers thought it better
to look at the sun.

Which makes sense,
given that most of what we see

when we look out into the cosmos
is stars.

The first attempts to analyse
the composition of the sun

were done with a set-up
rather like this.

Well, not exactly like this -

this is a cutting-edge
21st-century solar telescope.

But the basic idea
was exactly the same.

The basic idea's very simple.

The sun's light is reflected off
this mirror here,

up into a second mirror...

where it bounces off,
down through the top of the tower,

all the way to the bottom,
ten storeys down,

where it's focused and split
into a spectrum and analysed.

This is the control room
of the solar telescope.

The base of the telescope
is over there.

And here, I've got
a live feed image of the sun.

And what I've got up here
is a zoomed-in section

of the spectrum of the light
coming from the sun.

Now, it's in black and white,

but it actually corresponds to
the green part of the spectrum.

These two thick dark lines
correspond to the element iron.

They tell us
there's iron in the sun.

Now, here I have the spectrum
in much more detail,

and these two lines correspond to
these two dips

in the absorption spectrum

at very specific wavelengths.
This is iron.

If I look at different parts of the
spectrum, I can see other elements.

This big dip here is hydrogen.
These two dips represent oxygen.

And this dip corresponds
to the element magnesium.

All these dips and lines
in the spectrum

indicate the presence of these
elements in the sun's atmosphere.

Effectively, a fingerprint
of the sun's composition.

To a geologist, these elements
are all very familiar.

It appears, at first glance, that
the sun is made of the same stuff

as the Earth, that the sun is simply
a very hot rock.

And that would have been that

were it not for the insight
of Cecilia Payne.

She realised that the spectrographs
were being affected by processes

in the sun's atmosphere.

These would distort the apparent
abundance of the elements

that make up the sun.

So, she recalculated the relative
abundances of the elements

and discovered that the sun
was composed almost entirely

of just two elements -

hydrogen and helium.

All the other elements -
carbon, oxygen, sodium, iron -

that made the sun seem so Earth-like

amounted to just a tiny fraction
of its composition.

When she first presented
this result,

it was considered impossible.

In fact, when she wrote up her work,

she was persuaded to add the comment
that these calculated abundances

of hydrogen and helium
were almost certainly not true.

The idea was only accepted
some four years later,

when the director
of a prestigious observatory

arrived at exactly the same
conclusion by different means.

Ironically, this director was
the very same man

who'd initially dismissed
Payne's work as clearly impossible.

Payne's revelation about the ratio
of hydrogen and helium was found

to be remarkably consistent for
almost every star in the galaxy.

That led to a big conclusion.

The universe is dominated by just
two elements, the simplest

and lightest elements -
hydrogen and helium.

Together, they make up more than 98%
of all the matter in the universe.

All the other elements that are
so important to us -

like carbon, oxygen, iron -
amount to less than 2%.

So now the challenge for supporters
of the Big Bang theory

was very clear and simple -

could the Big Bang theory
explain the creation

AND the observed ratios of hydrogen
and helium found in the stars?

But to answer that would require
a fundamental shift of emphasis.

Rather than consider the almost
infinite vastness of the universe,

it was necessary to consider

the infinitesimally
small world of the atom.

And that required,
not an astronomer,

but an entirely different
kind of physicist.

George Gamow was
a Russian nuclear physicist

and an enthusiastic advocate
of the Big Bang idea.

He turned his attention to the
earliest moments of the universe.

Here, he felt,

was where the answer to the
composition of the universe lay.

This was when he believed hydrogen
and helium were first forged,

and he proposed it would have
happened very soon

after the birth of the universe.

He set about building
a mathematical model

of the earliest stages
of the universe.

He was thinking about the universe
in terms of seconds and minutes,

rather than billions of years.

And he recruited a young protege,

this chap, Ralph Alpher,
to help him.

After years of hard work,
some of which, according to Alpher,

were aided by hard drinking
in a bar,

they presented their idea.

By rewinding the universe,
it was clear to them that there

would have been a time when the
early universe was incredibly dense

and phenomenally hot.

At this stage, which they calculated
to be just three minutes

after the Big Bang, the universe
would have been so hot

that atoms themselves
couldn't exist,

only their constituent parts,

a kind of superheated
primordial soup

of protons, neutrons and electrons.

They even gave this soup
a name - ylem,

from an old English word for matter.

Then came the crucial moment...

a time when conditions were right
for the nuclei

of the first elements to be forged.

In a short period of time,

which they estimated to be
less than 15 minutes,

hydrogen nuclei proton were
coming together to form helium,

in the process of nuclear fusion.

Moreover, the ratios of hydrogen
and helium predicted by their model

matched that measured in the stars.

They announced their results
in a paper published in 1948.

However, Gamow added another
author to the paper -

the famous nuclear physicist,
Hans Bethe,

who had nothing to do with the work.

Gamow added his name for a laugh.

He thought it made
a good science pun,

because the authors of the paper now
read, "Alpher, Bethe and Gamow."

The young Alpher, however, was less
amused to be sharing the credit

with someone who'd done no work.

By way of reconciliation,
the story goes,

Gamow produced a bottle
of Cointreau for Alpher

but with the label changed to read,
"Ylem."

The ability to make calculations
that explained the origins of matter

in the first few minutes after
a Big Bang was remarkable in itself.

But there was
a very significant prediction

that emerged from their work.

A prediction that had the potential
to deliver the proof

that the universe had begun
with a Big Bang.

Alpher continued to study
the early evolving universe,

focusing on what happened next.

He pictured the universe
at this stage as a seething fog

of free electrons and atomic nuclei.

Then it dropped
to a critical temperature,

a temperature cool enough
for electrons to latch on

to the nuclei of hydrogen
and helium.

At this precise point,

light was released to travel freely
throughout the universe.

The first light of creation.

This might have remained nothing
more than an academic curiosity

had it not been
for Alpher's insight.

You see, he realised that
this light from the beginning

of the universe should
still be reaching us now,

after billions of years.

Very weak, very faint,
but observable in all directions.

He calculated that the expansion of
the universe should be stretching

the wavelength of this light beyond
the range of the visible spectrum

and should now be arriving
as microwave radiation.

So, find this predicted ancient
microwave signature

and it will prove, not just the
theory of the early evolution

of the universe, but the entire
Big Bang theory itself. Simple.

The problem was,
this was the late 1940s

and no-one had any way of
detecting such a weak signal.

The acid test was quietly forgotten.

Supporters of the Big Bang
now had the prediction

and observation
of an expanding universe.

And a theory for
how elements were forged

in the first few minutes
after the Big Bang.

But without the clinching evidence
for this, the argument over

whether the Big Bang theory
was correct rumbled on.

The opponents of the Big Bang
continually tweaked and adjusted

their theories to make their idea
of an eternal and infinite universe

fit the new observations.

The scientific community
was still pretty evenly split.

Conclusive proof of the Big Bang
theory would eventually emerge

some 15 years later.

It would be revealed
quite unexpectedly

by two young radio engineers.

In 1964, Arno Penzias
and Robert Wilson -

that's Penzias on the right there -

discovered something so momentous,
it won them the Nobel Prize.

This telescope is dedicated to
study their accidental discovery.

In 1964, Penzias and Wilson were
working at the Bell Laboratories

in the US where they were
given this, a bizarre

and obsolete piece of kit
to play with.

It looks, for all the world,
like an enormous ear trumpet.

But when they turned
their telescope on,

they found that the sky was
saturated with microwave radiation.

All warm bodies emit
microwave radiation,

whether it's from the atmosphere
or from the instrument itself.

And today's mobile communications
flood the sky with it.

FAINT STATIC

So, before they could do
any useful measurements,

they had to calibrate
their Horn Antenna to see

if they could reduce this "noise."

FAINT STATIC

Even after accounting
for the atmosphere

and their instrumentation -

of course, there were no mobile
phones to worry about back then -

they were still left
with this persistent

and deeply irritating
background noise.

It was registered on
their instruments as a radiation

with a constant temperature of
three degrees above absolute zero,

a microwave hiss that
they couldn't get rid of

no matter what they tried.

FAINT STATIC

Even more annoying for them
was the fact that it seemed to be

everywhere they pointed
their celestial ear trumpet.

They were about to give up
when Penzias attended a meeting

where he casually mentioned
this irritant to a colleague.

A few weeks later, the same
colleague phoned him up and said

he knew of some researchers
in Princeton

who are looking for
just such a signal.

Unwittingly, Penzias and Wilson
had stumbled upon

that predicted radiation -
Alpher's burst of light

from the early evolution
of the universe.

Here, at last, was proof
of the Big Bang theory.

It's quite remarkable to think
that this microwave radiation

has travelled across
the furthest reaches of space,

from 13.8 billion years ago

when that first light from
the Big Bang was released.

As Penzias himself said,
when you go outside,

you're getting a tiny bit of warmth
from the Big Bang on your scalp.

And, yes, I probably feel it
a bit more than most.

Almost 40 years after Lemaitre
first postulated it,

the idea of the Big Bang had finally
entered the scientific mainstream.

But the discovery of this cosmic
microwave background radiation,

the CMB, and the proof
of the Big Bang theory itself,

isn't the end of our story.

We've probed back to the first
few minutes after the Big Bang.

And beyond this lies
a new frontier of knowledge.

There are still very big questions
to resolve about the beginning

of the universe, questions like,

"Where did all the matter itself
come from?"

And "How do you get
something from nothing?"

The answers to these questions
lie further back,

hidden behind the curtain
of the CMB.

Their secrets lie
in the primordial universe,

within the very first second
of its existence.

This is where the edge
of our understanding now lies,

and this is where scientists
are focusing their efforts...

not by looking into the skies,

but here on the border
of Switzerland and France.

More specifically, at CERN,

with the largest particle
accelerator in the world,

the Large Hadron Collider, or LHC.

Now, you might be wondering what a
particle accelerator has to do with

the early universe, because
the connection between the two

is far from obvious.

The thing to remember is that,
when the universe was very young,

it was much smaller
and so all the matter -

everything that makes up the stars,
the galaxies, black holes -

all had to be confined
into a much smaller space.

At that stage, the universe
was phenomenally hot and,

more significantly,
its energy density was very high.

It was then that the first matter
sprang into existence.

The LHC can't yet replicate
that process...

..but it can allow us
to study the properties

of these fundamental particles.

Once a year, the LHC stops
its normal business of colliding

beams of protons, and instead uses
much more massive particles

to create collisions with
energies more than 80 times greater

than that produced from two protons.

They do this by accelerating
atoms of lead,

stripped of all their electrons,

up to speeds close to that of light,

and smashing them together.

And that lets us
see something pretty special.

The collisions are
so intense that, for a moment,

we create something unique -

a world not of atoms
or even neutrons and protons -

but of quarks and gluons and
leptons - exotically named particles

that came together to form atoms
in the first millionth of a second

after the Big Bang, and have been
locked away ever since.

Down there, underneath that lead
shielding, we're recreating a stage

in the universe's evolution
called the quark-gluon plasma.

Now, this is the moment immediately
before the quarks become trapped

by the gluons to create protons
and neutrons,

which themselves go on
to form the nuclei of atoms.

The phrase we use - grandly -

is the confinement of the quarks.

To develop the necessary energy,

the lead nuclei are passed through
a chain of smaller accelerators,

gradually ramping up the energy
until they're finally

fed into the largest accelerator
on Earth, the LHC.

Now, the maximum energy a beam
can achieve is directly related

to the size of the accelerator,

and the LHC has
a circumference of 27km.

That means the beams here
can achieve an energy

of 1,000 tera-electronvolts.

Now, actually, that's less than
you might imagine, because

it's equivalent to the energy
that a housefly hits a window pane.

But the critical difference here

is that the energy is concentrated,

it's the energy density
that's important.

The LHC can squeeze all that energy
down to a space that's less than

a trillionth of the size
of a single atom.

This is something that can happen
nowhere else in the known universe.

The two beams of lead nuclei
are travelling around the ring

in opposite directions.

They're meeting deep underneath
this control room at the detector.

We can see live feed pictures
of the detector up on that screen.

Now, underneath us,

they're travelling at a speed
of 99.9998% the speed of light.

That means they're covering the full
27km circumference of the ring

more than 11,000 times per second.

When the beams reach
maximum energy -

and we can see up there, it says
"iron physics stable beams" -

that means they can be crossed.

Just like in Ghostbusters.

At that point, a tiny fraction
of the lead nuclei will collide

and create a super-hot,
super-dense fireball

with a temperature 400,000 times
hotter than the centre of the sun,

and a density that would be
equivalent to squeezing

the whole of Mont Blanc
down to the size of a grape.

That looks like
a fantastic image there.

Can you tell me what we're seeing?
It's amazing, actually, isn't it?

It's literally tens of thousands of
particles and antimatter particles

flying out - this kind of aftermath
of this explosion. Right.

So the coloured particle trails here

AREN'T the quarks and gluons
themselves,

but evidence of the quark-gluon
plasma created by the collision.

We have to infer its properties
from looking at the debris

that flies out. It's a bit like
working out how an aircraft works

by looking at the debris of
a plane crash. That's what we see.

What I find amazing is, what we're
doing here is trying to recreate

that moment in the early universe
where the quarks and gluons

were all free to float around,
cos the energy was so high,

and then it cooled and they stacked
together. You're doing the opposite.

We're starting with normal matter,
smashing it together,

and going back to that
unconfined state, that plasma.

Yeah. I like to think about it
as a time machine.

We're actually winding back
the clock.

And this is the only way that we can
study the properties of free quarks,

because these quarks have been
imprisoned inside particles

like protons and neutrons
for 13.8 billion years.

That's pretty incredible, isn't it?
Finally, after 13.8 billion years,

you can set these quarks free -

even if it's for a fraction
of a second. Yes.

While we don't yet know
how matter sprang into existence,

studying these collisions allows us

to make the first tentative steps
towards that discovery.

What we've just witnessed is
the earliest stages of the universe

that anyone - anywhere -
has been able to observe.

It's the closet we've got
to the moment of the Big Bang.

And, let's face it, it's not bad.

One millionth of a second
after the Big Bang itself.

Even going this far back in time

still leaves physics
with unanswered questions.

Beyond this is where some of the
deeper mysteries of the universe

are hiding. How the fundamental
forces that bind matter together -

gravity, electromagnetism
and the nuclear forces -

are connected to each other.

How the particles
that make up matter itself

condensed out of a fog of energy.

How mass is generated from
the force that binds protons

and neutrons together.

And how the universe itself
underwent a super-fast expansion

in one billion-billion-
billion-billionth of a second

to create the structure
of the cosmos.

At the moment, we have no way of
observing any of these phenomena.

This is the realm of abstract theory
and speculation.

If we're ever going to replicate
this early stage of the universe's

evolution, we're going to need to
create considerably higher energies.

Frankly, we're going to need
to build a bigger collider.

And that's a problem.
And it's not just one of expense,

although it would be
phenomenally expensive.

No, it's more one
of finding the room to build it.

Remember when I said the energy's
related to the circumference

of the accelerator?
Well, the LHC, down below me,

has a circumference of 27km.

It runs beneath the Jura Mountains

and straddles both France
and Switzerland.

In order to look back and observe
the universe at this earliest stage,

well, we'd need to build
an accelerator

with a circumference larger than
the orbit of Pluto.

Revealing the origin of the universe
begs another,

even more profound question -

how will it end?

Next time, I discover whether
the universe will end with a bang

or a whimper.

Want to discover more about the
beginnings of the universe?

Go to the address below and follow
the links to the Open University.

We know the universe had a
beginning.

A moment 13.8 billion years ago
when it sprang into life...

..creating the vast cosmos we see
today.

Now we've discovered its origin,

we're faced with another equally
fundamental question.

If the universe has a beginning,
if it was born,

does that then mean it'll
eventually die?

Or will it just keep on going for
ever, eternal?

You see, for us, as all-too-mortal
humans, the ultimate fate

of the universe is a question that's
hard-wired into our psyche.

Trying to answer it has
driven an astonishing

revolution in our understanding of
the cosmos.

Yet in recent years, it's also
revealed a universe

that's far stranger than we ever
imagined.

And led to one of the most shocking
moments in scientific history.

It's the latest twist in a tale
stretching back over 100 years.

In that time, key experiments and
crucial discoveries...

And there it is.

Exactly, exactly where Hoyle
predicted.

..have brought us closer than
anyone thought possible

to finally knowing the ultimate
fate of the universe.

The sheer scale of the universe is
truly staggering.

How on earth can you predict the
future of something so vast...

..so complex...

..so much bigger than we are?

Since we first started grappling
with this question,

the answer has hinged on one simple
idea.

If we could chart, observe and
understand how the universe has
changed,

how it has evolved to the present
moment from its very

ancient beginnings, then we should
be able to extrapolate forward

and predict how it will evolve in
the future.

Unfortunately, the slight flaw in
that plan is that

the universe operates on timescales
of millions and billions of years.

We don't.

To understand the workings of the
universe,

we need to see beyond our
limited human lifespan.

And in this case, it turned out the
sheer scale

of the universe could be turned to
our advantage.

The universe is so vast,

light from some of the objects
we see in the night sky

has taken millions, even billions
of years to reach the Earth.

When we look up, we're looking
back in time at a record

of the deep history of the universe.

The problem is, we only have a
snapshot, a single complex

and confusing picture of all this
history.

It's like taking all the words in a
novel, jumbling them up

and sticking them on a single page.

The key is to try and unpick this
story, to learn how to read it,

to recognise and understand what's
going on.

Astronomers realised that stars
could help unlock that history.

If scientists could work out
how stars change,

how they evolve in time,

they could begin to understand the
bigger story of how the universe

was changing, the first clues to
what the future might hold.

But it would take until the middle
of the 20th century

to find the answer.

Unlocking the secrets of the stars
would take

a moment of brilliance from this
man, Fred Hoyle.

Hoyle was a brilliant mathematician
and physicist,

one of the greatest of his day.

He was creative, coming up with bold
theories.

Above all, he loved a problem,

some thorny issue he could make his
mark by solving.

And in the late 1940s, he found one
of the biggest.

Hoyle wanted to know where
the elements came from.

The early universe was mostly just a
sea of hydrogen and helium.

The simplest and lightest elements.

But we know that changed.

Look around us now. This is no
simple world we live in.

We're surrounded by complexity,
built from complex, heavy elements,

like the oxygen I breathe
and the iron in our blood.

And of course, carbon, in the trees
and in every cell in my body.

No-one knew how to bridge the gap,
how the universe

went from that very simple
beginning to all of this.

This was the problem
Hoyle seized on.

Hoyle knew nuclear fusion must
hold the answer.

In nuclear fusion,

lighter elements are fused together
to make more complex ones.

It was already known to happen in
the heart of stars,

where hydrogen fused together to
form the more complex helium.

Hoyle wondered how to go further,
how the helium nuclei

might fuse to make heavier
elements.

It's a remarkably simple idea.
Here's our helium nucleus.

If you could stick together two
helium nuclei,

you'd make beryllium, a heavier,
more complex nucleus.

Then, add a third helium nucleus
and you get carbon.

From there, you can carry on
building up heavier and heavier
elements.

It sounds like the perfect solution.

But there was a very good reason why
the formation of carbon -

hence all other elements -
was still such a big mystery.

The problem was, that the physics of
this process just didn't work.

Calculations showed that three
helium nuclei wouldn't stick
together.

The carbon nucleus they formed was
unstable and simply fell apart.

If it broke down at carbon,

then there was no chance of making
any other heavier elements.

It was like hitting a roadblock,
every time.

In typical bold and bullish fashion,

Hoyle got around the problem by
predicting a brand-new state of
carbon.

Hoyle took an intuitive leap.

He decided that if three helium
nuclei did come together inside a
star,

they could form carbon with a bit
more energy than normal.

In this special state, it could stay
intact for just long enough to
become stable.

In that way, stars could make carbon
and the roadblock was removed.

If he was right, then Hoyle had
solved the mystery.

The elements were built in the heart
of stars.

But there was more at stake
than that.

Hoyle realised his theory could
reveal how stars changed

through their lives.

And as the universe we see is built
of stars, that would make it

a powerful tool for predicting
the future of the universe.

Astronomers were already grouping
stars based on their size,

colour and brightness...

..plotting them on a chart that was
known as the Hertzsprung-Russell
diagram.

So here we had the diagram that
they created.

Along here is size and brightness,
running from very large,

very bright stars, all the way down
to smaller, dimmer stars.

And along this direction is
colour and temperature.

Very hot blue stars, all the way
down to cooler red stars.

Most regular-size stars fell into a
long diagonal

through the middle of the diagram,

with a group of giant,
bright stars above

and small, dwarf stars below.

Astronomers could see the patterns,
but weren't able to unlock what they
meant.

Until Hoyle and his theory presented

a radical new way
of looking at the diagram.

One that would reveal
the life cycle of a star.

Let's consider our own sun.

Now, at the moment, it's sitting
here in the middle of the diagram,

happily burning hydrogen,
turning it into helium.

But if Hoyle was right, when it's
run out of its hydrogen,

it'll start fusing helium to make
heavier elements.

Now, at this point, a dramatic
transformation takes place.

Because rather than moving down
the diagram in this direction,

it expands to many times its size

and jumps across here to live
amongst the red giants.

At this phase, it starts burning
helium to make much heavier

elements until it finally begins to
produce carbon.

Now, at that point, when it's run
out of its nuclear fuel,

it undergoes its final
transformation.

It sheds most of its outer layer
and leaves behind a tiny white
cinder,

living here amongst
the white dwarfs.

All stars follow their own
route around the diagram.

Hoyle's theory provided the
understanding to track each
star's evolution,

driven by the sudden ignition of a
new phase of elemental formation.

Here was the answer to the mystery
of the heavy elements.

The key to the life
cycle of the stars.

And a window onto the future
of the universe.

All thanks to Hoyle's new
state of carbon.

There was just one slight problem.

No-one had ever seen or detected
Hoyle's special form of carbon,

not in a telltale spectra from
stars, not anywhere on earth,

not even in a laboratory experiment.

As far as anyone could tell,
it didn't exist.

And without this special
form of carbon,

the whole theory would
come crashing down.

What happened next is a testament
to Hoyle's brilliance

and almost pig-headed self belief.

In the 1950s, Hoyle joined the
California Institute of Technology -

Caltech - who had one of the few
particle accelerators

in existence at the time,
similar to this one.

Hoyle wanted to use the accelerator
to try

and make his high-energy carbon.

They were not so keen.

Here was an unknown Brit trying to
take over their new machine

in order to look for something he'd
effectively made up.

Like Hoyle, I'm a theorist.

Experimental physics is a very
different world

and it's a different
area of expertise.

But Hoyle had the confidence, the
daring, to stride into the lab

and, as the director
of the facility said,

without a buy-or-leave, demand that
they give up the research

they were doing in favour of
carrying out a complicated
experiment

to look for something that no-one
even believed existed in the first
place.

I'm pretty sure I wouldn't have had
the guts to do that.

Hoyle kept at them, arguing it would
be a crucial and famous discovery.

Finally, they gave in.

The search was on.

Today, I'm recreating
their experiment.

The plan was to bombard a target
element with a particle beam

to see if they could create that
state of carbon.

Well, I have with me my own
experimental colleagues,

Zahne and Robin, to help me out.

Our target will be held in the
centre of this reaction chamber.

Now, what they were looking for was
a very specific signal

that would show up
in their detectors.

If that state of carbon existed,
then Hoyle predicted that it would

show up as a spike in the energy
at 7.7 million electron volts -

the fingerprints of this special
state of carbon.

We'll be looking for the same
spike in energy.

Time to seal the chamber...

..close the radiation doors...

..and see for ourselves what
happened.

Right, this is the control panel.

And they've let me in - a theorist -
to get it all running.

So the first thing I do is fire up
the beam.

Then to aim the beam
at the target.

Charged particles are now
slamming into the target.

Back in the 1950s, this was Hoyle's
moment of truth.

Now data will start coming in
and the important display

to look at is over here.

Now, if Hoyle was right, they'd see
his excited state of carbon at this

energy here. They would expect to
see a spike in energy at that point.

And there it is.

Exactly - exactly -
where Hoyle predicted.

Now, when this experiment was
carried out some 60 years ago,

they were flabbergasted to see that
Hoyle was right.

It's quite incredible to think that
he just worked on a theoretical
hunch,

convinced his experimental
colleagues to do the experiment,

and he was right.

He was also right about the fame.

The director of the laboratory
went on to receive

the Nobel Prize for the discovery.

Hoyle, however, received nothing.

They published their findings
in one of the most famous

and heavily referenced papers
in science.

On the front cover of the paper,

the authors put a very apt quote
from Shakespeare's King Lear.

"It is the stars, the stars above
us, govern our conditions."

It was the confirmation of this
excited state of carbon that

proved that it's inside stars that
all the elements that make

up the world around us, including
ourselves, are actually forged.

And with that discovery, we gained
real insight into the life cycle of
stars.

We could begin to understand how
the universe changed over time,

both now and into the future.

Here was the foundation for
extrapolating into the future.

And it made one clear prediction
for the end of the universe.

It was hydrogen and helium that
first formed stars,

and it was these two elements
that were consumed in stars

as they aged, creating all the
heavier elements in the process.

The logical conclusion
was disturbing.

After an almost unimaginable
length of time,

stars would use up all the hydrogen
and helium in existence.

No new stars could form,

and existing stars would eventually
run out of their fuel and die.

The universe would go dark.

For everything that's important to
you and me, the light and life

created by the stars, the universe
would eventually come to an end.

But there was another option.

One that promised
a very different fate...

..and would play out long before
the stars ran out of fuel.

A fate that involved a fundamental
force of the universe.

Gravity.

The potential for gravity to
define the ultimate fate

of the universe was first spotted
by one of science's unsung heroes.

Vesto Slipher.

Little-known, his pioneering
expert measurements

would transform our understanding
of the universe.

In the early 1900s, astronomy was
entering its golden age,

with evermore powerful telescopes
trained on the skies.

One of the biggest targets
of the time was the nebulae.

Nebulae were patches
and swirls of light

that could be seen
in between the stars,

and not much was known about
these mysterious objects,

so astronomers were scrambling to
find out as much about them as
possible.

Slipher was interested in one
particular aspect of the nebulae -

their motion.

And for his target, he chose the
most famous one of all, Andromeda.

Slipher wanted to be the first to
measure how quickly a nebula was
moving.

The problem was, his was not
the best telescope out there.

Not by a long chalk.

But Slipher did have one big
advantage over his competitors.

He was a superb astronomer.

This telescope is actually the same
size as Slipher's.

It has a 24-inch mirror.

But Slipher would have loved to have
got his hands on something like
this.

You see, what he needed was to get a
spectrum.

Now, that involves splitting
the light from the nebulae

into its different wavelengths, the
different colours that it's made of.

Now, he'd have used something like
this - it's a diffraction grating.

I can see it reflects this light
and gives me

all the different colours of the
rainbow.

What worried Slipher was that he
needed to collect as much light as
possible

to give him a usable spectrum, and
nebulae are exceptionally faint.

He feared that getting enough light
from his telescope would

prove to be impossible.

It may be the same size,

but this modern telescope can
capture the spectrum

of Andromeda in a matter of minutes.

With his telescope, Slipher needed
14 hours to produce one spectrum.

Two days of backbreaking efforts.

Seven hours each night,

constantly adjusting the telescope
to keep it fixed on Andromeda.

Slipher wanted to know how
Andromeda was moving,

and for that he didn't just need
the spectrum of light on Andromeda,

he needed to have
the absorption lines.

Now, these are discreet gaps
in the spectrum, like this.

Now, these absorption lines should
always be in the same place

if the source isn't moving.

If they've shifted to the right,
towards the red end of the spectrum,

that means that the source is
moving away from us.

If they've shifted to the left,
towards the blue end of the
spectrum,

that means the source is moving
towards us - a blue shift.

Now, after two days of observing,
Slipher was ready to develop his
photograph.

And he didn't get something as
beautiful and clean as this.

He got this image.

Now this is in fact blown up.

In fact, what he got was a much
smaller image than this.

And it's not even these lines,
at the top and bottom.

In fact, what he got was this dirty
smudge in the middle.

That was the spectrum
from Andromeda.

Now, you might think he'd failed,

that you couldn't get anything
meaningful from this.

In fact, not only was he able to get
a meaningful measurement,

he could work out that Andromeda
showed a very clear blue shift,

that it was moving towards us.

In fact, he worked out it was moving
towards us at a speed of 300km per
second,

which actually matches
modern-day estimates.

Slipher had done it.

The first ever measure
of the speed of a nebula.

His skill and tenacity overcoming
the limits of his telescope.

When Slipher presented his findings
at an astronomy meeting in 1914,

he received a standing ovation.

It's often easy to forget how
important people like Slipher are.

The major breakthroughs
in science aren't always about

the big idea or
the beautiful theory.

They're often simply reliant on
people who are exceptionally

skilled at observing and measuring
the natural world.

We now know that the Andromeda
nebula is actually a galaxy

like our own, the Milky Way.

And it's Andromeda's movement that
reveals how gravity can shape

the fate of the universe.

Since it was first born
in the Big Bang,

the universe has been
expanding outwards.

As a result, most galaxies
are actually

heading away from each other.

When they first formed, the same
would have been true

of Andromeda and the Milky Way.

Until gravity got to work and began
to overwhelm that expansion.

It's gravity that's dragging
Andromeda

and our own Milky Way galaxy
inexorably together.

The question is, if it can pull off
this trick in our own little corner
of the cosmos,

can it do the same over the entire
expanse of the universe?

If gravity could overwhelm
the expansion,

then long before the stars are
burnt out,

our vast universe would inevitably,
inescapably collapse in on itself.

The universe would end with
a big crunch.

If gravity failed, the universe
would simply continue to expand,

far beyond even the time
when the last star had died.

Everything hinged on one factor,

predicted by Einstein's
general theory of relativity.

Using general relativity

revealed that there were two very
different futures to the universe.

What's more, they were able to
calculate a specific figure

that marked the boundary between
these two different scenarios.

It became known
as the critical density.

The critical density was
effectively a threshold

based on how much matter
and energy - how much stuff -

there was in the entire universe.

If that total was above
the critical density,

then gravity would drag
the entire universe back together

into the Big Crunch.

If the total was below
the critical density,

then the expansion of the universe
will continue for ever.

The fate of the entire universe
came down to a simple question -

what universe do we live in?

One that is above the critical
density, or one that is below?

One way to tell was to look at
the expansion of the universe.

If the universe was above the
critical density and heading for

collapse, then the rate of expansion
would already be slowing down.

So, astronomers began working on
a way to measure

how the expansion
of the universe was changing.

They were confident until
a precocious PhD student

called Beatrice Tinsley spotted
a fatal flaw in the plan.

Tinsley, know as "little beetle"
to her family and friends,

was an extremely talented musician.

She could have turned professional.

But instead she decided to focus on
her other great passion,

which was astrophysics.

Here, too, she excelled.

But an academic career in the 1960s,
if you are woman, wasn't easy,

and her institution,
the University of Texas,

seemed determined to ignore this
brilliant scientist in their midst.

Despite that,
she completed her PhD

in less than half the time
it would normally take.

And that PhD spelled trouble for
the expansion rate measurements.

The plan was to measure
how galaxies were moving

at different distances from Earth

and therefore at different
times in the past.

How their movement changed

would reveal how the expansion
of the universe was changing.

Measuring the movement was
relatively straightforward.

It was measuring the distance
where the problem lay.

In our everyday world,
we're surrounded by visual clues

that give us a good sense of scale,
and therefore of distance.

But in the vastness of the universe,
this is much more difficult,

so astronomers turned to something
that might seem unusual.

Light itself.

Light is not perhaps
an obvious tape measure,

but in this case it seemed ideal.

Now, this relies on
a very simple principle.

How bright the light appears to me
is dependant on how close I am to it

so when I'm very close,
a lot of light enters my eyes

and it seems bright.

But as I move away, the light has
had more chance to spread out

and less of it enters my eyes,
so it appears dimmer.

Crucially, this change
in the level of brightness

follows a very precise
mathematical relationship.

And I can use this relationship
to calculate distance.

'If I measure the difference
in brightness

'between a light next to me...'

220.

'..and one further away...'

About 1.5.

I don't know if you can see that.
It's quite dark.

'..I can work out how far away
the light is.'

And so now I have to divide
these two numbers.

Well, it's roughly 150.

Now I have to take the square root.

The square root of 150...

Well, it's about 12.

It's just over 12.

About 12.2 metres.

Right.

Now to check my working.

It's this principle
that astronomers were using

to measure the distance to galaxies.

So, what I have here...

is 11.5 metres.

It's a bit less than the 12 metres
I calculated, but close enough.

I'm pretty happy with that.

But this technique only works

if you know how bright
the distance object should be,

so you can measure how much
that brightness has changed.

And that would turn out to be
the astronomers' Achilles heel.

They were measuring galaxies
at different distances,

so at different times
during the life of the universe.

This meant that the galaxies
differed in age by millions

or billions of years.

You see, for the distance
measurements to work,

they had to assume that all these
galaxies of different ages

were shining with the same
brightness.

In other words,

a galaxy's brightness
doesn't change over time.

But for Beatrice Tinsley,

there was a fatal flaw
at the heart of this assumption.

Tinsley was fascinated by
the life cycle of the stars -

how they changed
through their lives.

Her PhD looked at what effect
that would have

on the brightness of galaxies.

For Tinsley, it was clear that
if stars have a life cycle

during which their appearance
and brightness change,

then because galaxies
are fundamentally made of stars,

so too would their brightness
change over time.

Tinsley's findings sent shockwaves
through the field.

"A palpable sense of panic", as one
astronomer of the time described it.

And they were immediately
challenged.

You see, a huge amount of time,
effort and money

had been invested in these
expansion measurements

and yet here was this unknown young
PhD student - a woman, no less -

who was questioning it all.

And yet there was no arguing
the logic of Tinsley's work

and, after four years,
it was eventually accepted.

With that, it was back
to the drawing board.

A new way was needed to test
how close the universe was

to the critical density

to see if it would collapse
or continue to expand.

There was another option.

A more direct approach.

One obvious way to see how close
the universe is

to the critical density

is just to count how much stuff
there is out there.

It's a simple enough idea,
but rather difficult to pull off.

After all, in something as almost
unimaginably vast as the universe,

how do you count every galaxy,
every star,

every speck of interstellar gas?

It's almost impossible.

So, instead, astronomers cut
the universe down to size.

They took an average count
of just one small part

and then multiplied it up
from there.

They could do this thanks to one
unique characteristic

of the universe.

As far as we can tell, the universe
is, on the largest scales,

the same in whatever direction
we look.

So an astronomer sitting on Earth
looking out into space

will get pretty much the same view
as an alien astronomer

on a planet
thousands of light years away

looking out in a completely
different direction.

And that's why measuring
how much stuff there is

in one small part of the universe

gives us a pretty accurate measure
of how much there is overall.

They took their averages and came up
with a total amount of mass

and energy in the universe.

The results took everyone
by surprise.

All of them suggested the universe
was well below the critical density.

In fact, the best estimate suggested
the universe had so little mass

that its density was only a tiny
fraction of the critical value.

Obviously, if right,

there was no way that the universe
was going to collapse.

But there was a problem
with this first estimate

of how close the universe was
to the critical density.

The results were so low,
they just didn't make any sense.

A flat white coffee, please.

Ours is so clearly a universe
of matter, mass and energy.

They dominate our world.

They ARE our world.

These findings painted a picture
of a universe

so alien to our everyday experience
that it is perhaps understandable

it was such a difficult concept
to embrace.

What's more, the estimates seemed to
be at odds with the universe itself.

The scale of the mismatch
was revealed

when the universe was mapped
on an unprecedented scale

by Margaret Geller
at Harvard University.

What Geller and her team did was
first take a slice of the universe

some 500 million light-years long,
300 million light-years wide,

but still a thin wedge
of the visible universe.

They observed as many galaxies
as they could

and plotted them against distance.

So, every one of these dots
is an individual galaxy.

There's over a thousand of them.

What took everyone by surprise
was this pattern that they saw -

these bubbles, or almost
a honeycomb structure.

You see, everyone had assumed
that the galaxies would be

scattered randomly
throughout the universe.

Here, for the first time, was
evidence that - far from random -

the universe actually had structure.

And at the heart of this
newly-discovered structure

was the pull of gravity.

Since almost the beginning
of the universe,

gravity has been drawing
matter together.

First into clouds of gas, which then
clumped together to form galaxies.

These galaxies come together
to form clusters of galaxies

and the clusters into superclusters.

It looks like a work of art.

These superclusters of galaxies
are all joined together

by filaments of dust and gas,

all acting under the same
irresistible pull.

My universe has just collapsed.

Argh!

Here we clearly see gravity
acting as an architect,

shaping and influencing
the structure of the entire universe

on a truly cosmic scale.

No, I think I can do better.

'The problem was, the estimates
of matter in the universe

'were so small...'

Open that up.

'..they put the universe
so far below the critical density,

'that such grand structures
simply could not form.'

I don't like that.

'According to the numbers,

'the universe as we know it
couldn't exist.'

This is a rubbish universe.

There had to be something missing
from the counts.

But what was it?

And what would it mean
for the critical density

and the fate of the universe?

One of the most colourful
and controversial scientists

of the 20th century
found the first clue.

Fritz Zwicky.

Zwicky was an eccentric, abrasive
and brilliant scientist,

known occasionally to refer
to the rest of his profession

as "spherical bastards", which is
basically anyone who's a bastard,

whichever way you look at him.

But even those who disliked him

had to admit that he was capable
of brilliant work.

Zwicky was also looking at
galaxy clusters

and they would lead him to discover
something extraordinary.

This picture here
is just such a galaxy cluster.

It's called Abell 1689.

Each one of these yellow dots
is part of the cluster.

It's quite incredible to think
that each one of them

is an entire galaxy in itself.

It sort of gives you an impression
of the sheer scale of these things.

Zwicky was fascinated by what held
the clusters together.

The answer, of course,
has to be gravity.

Imagine these marbles are all
each individual galaxies,

moving in chaotic orbits around
the centre of the cluster,

but none of them moves fast enough
to be able to break free

and escape from the cluster.

Because of that, Zwicky could use
how fast they were travelling

to measure the strength of gravity
holding them in place.

And the strength of gravity
would tell him how much matter -

how much stuff -
there was within the cluster.

That is where things got
very strange,

because the galaxies were moving
at tremendous speeds.

The strength of gravity needed to
hold all these speeding galaxies

within the cluster required
far more mass than he could see.

And it wasn't just
a small difference.

In fact, he needed something like
a hundred times more mass

than could be detected.

Zwicky called this mysterious mass
Dunkle Materie.

Dark matter.

Here was a strong candidate for
the missing mass of the universe.

But to know if it took the universe
above or below the critical density,

they had to solve one major problem.

How to study something when there
is no known way of detecting it.

The answer would come thanks to
a discovery made here

at the Jodrell Bank Observatory.

This giant dish is
the Bernard Lovell Radio Telescope

and, in 1973, it spotted something
no-one had ever seen before.

At the time, it was carrying out
a survey of some very distant,

very bright objects -

quasars.

Part way through the survey, they
detected something very unusual.

I've come here today to take
another look at what they saw,

this time using not just
the telescopes here at Jodrell,

but radio telescopes
across the country.

Right, here we are -
the control room at Jodrell Bank.

A lovely view there
of the Lovell Telescope.

Now, over here, on these screens,

we see live data coming in
from various telescopes.

One of them, the Mark II, is a
radio telescope at Jodrell Bank,

but the rest are scattered around
the country, all linked together

through optical fibres feeding
into the central computer here.

The point is, the longer you observe
an object, the better-quality image

you get, and after 50 hours of
observation, here's what they see.

This is the same image
as was seen 40 years ago,

showing these two bright dots -

two quasars.

This wasn't the first time
quasars had been seen

but certainly the first time they
had been spotted so close together,

as though they were a pair.

A pair was something new.

They began to gather as much
information about them as possible,

including measuring their spectra -

the unique fingerprint
contained within their light.

Here are the spectra
from the two quasars.

Now, even at first glance,
I can tell they look quite similar.

In fact, they are much more than
just quite similar.

When they first measured them,

they saw that they were both
red-shifted -

so longer wavelengths -
by exactly the same amount.

And have a look at these
emission peaks.

They both fall at exactly
the same wavelength.

In fact, the spectra was so similar

they thought they had made
a mistake -

that they had looked at
the same object twice.

But they hadn't.

And that left just one possibility.

What they thought were two
separate quasars

were in fact just one single quasar

that had somehow been split
into two images.

A case of astronomical
double vision.

There was a theory
that could explain this -

a strange effect predicted
by Albert Einstein -

gravitational lensing.

If you look through this lens,

you see that everything behind it
is warped into strange shapes.

This bizarre effect is because,

as light passes through different
thicknesses of the glass,

it bends, giving rise
to a warped image.

Now, Einstein said that matter -
stuff - also warped space,

changing the very shape of
the fabric of the universe,

and so, as light passes
through regions of space

with high concentrations
of matter, it will bend,

just like it does going through
the glass of this lens,

and so giving rise
to similar visual tricks.

How much the light is bent

is dependent on how much
the space is being warped,

and that depends
on how much mass there is.

Between the quasar
and the telescopes,

there had to be
a huge amount of mass,

bending the light so much
that the image is split,

making the single quasar
appear as two.

Here's our culprit,
or at least part of it.

This smudge here is just one galaxy
within a cluster of galaxies

that sit between us
and the distant quasar.

So it's not just
a little bit of mass,

but hundreds of galaxies,
each with billions of stars.

Combined, they bend the light
from the quasar,

giving us the double image.

And the double image was crucial
to the study of dark matter.

Even with all the mass and matter
contained in the galaxy cluster,

there wasn't enough
to bend the light that much.

For that, you needed Zwicky's
mysterious and invisible

dark matter.

And carefully analysing exactly
how much the light was distorted

could reveal where
that dark matter was.

This is what you get - a map.

In the centre is the normal matter
of the galaxy cluster itself,

but, surrounding it, stretching out
much further, coloured here in red,

is the dark matter.

Look how far out it spreads.

It completely dwarfs the normal
matter of the galaxy cluster.

Zwicky's mysterious
and invisible matter

revealed by a cosmic
optical illusion.

It couldn't reveal
what dark matter was,

but mapping like this, as Jodrell
is still doing to this day,

did give an idea of how much
there was out there,

and it seemed to far outweigh
normal matter,

but was it enough to take the
universe over the critical density?

Even though there appeared to be far
more dark matter than normal matter,

that still seemed
to leave the universe

way below the critical density -

but this was still
far from the end of the story.

The discovery of dark matter

had taken the scientific community
completely by surprise.

Trying to work out how close the
universe was to the critical density

was just throwing up more mysteries
than answers.

A shocking new discovery
that initially promised

to finally reveal
the fate of the universe

instead threw physics into crisis.

In the 1990s, these telescopes were
part of an international project

looking to finally reveal
the fate of the universe.

They were using a new technique
to once again

look at how the expansion of the
universe had changed over time.

I've come to use this telescope -
the GTC -

to observe the object that was
at the heart of those studies.

This huge telescope - you can see
the vast mirror behind it -

is going to take a close look
at a supernova,

the explosive death of a star.

The light reaching us from these
distant epic events would be key

to unlocking how the universe
expanded in the past

and, in turn, would reveal what
would happen to it in the future.

To measure the expansion,

researchers were interested in
a particular type of supernova.

Our target tonight is the
same class of supernovae

that they were searching for -
a type Ia.

Now, what made type Ia
supernovae so useful

is that, when they went off,

they created an incredibly bright
spike of light.

Briefly, the star would shine
brighter than its entire galaxy.

Not only that,
but they always gave off

almost exactly the same level
of brightness.

This meant that not only could
they see them

over vast distances
and remote galaxies,

but they could also work out
exactly how far away they were.

So, if they could find
enough of them,

they could sample conditions
in the universe

over a wide range
of distances and times.

Tonight, astronomer David Alvarez
has been homing in

on a recently discovered
type Ia supernova.

Right, David, this is very exciting.
Do you have the supernova?

This is the image of the supernova.

That thing there? That thing there.

Can you zoom in at all on it?
Yeah, we can zoom in here.

You can see the bright dot.

And the rest of it is the galaxy?

The rest of the light
you can see there

is the host galaxy of the supernova.

I mean, that's incredible.

Here's a galaxy with hundreds
of billions of stars,

but this one exploding star -
this one supernova -

is shining brighter than the
whole of the rest the galaxy.

And you know how far away
this supernova is?

You've measured the distance?

Yeah, the supernova is about eight
billion light years away. Wow.

As well as the distance,

the spectrum of the supernova
is also crucial.

The astronomers needed
the spectrum of the light

because it gave them the redshift.

You see, as the light travels from
the distant supernova to Earth,

the universe is expanding,

the space the light is travelling
through is stretching,

and so the light itself
is also stretching.

Its wavelength is getting longer.

If it leaves the supernova

at a particular wavelength,
a particular colour,

when it arrives in our telescopes,
it's at a longer wavelength -

it's shifted towards
the red end of the spectrum,

hence a redshift.

So knowing the redshift
of the light

tells us how much space
has expanded in that time.

In a sense, it gives us a measure
of how big the universe has become.

Because of this, measuring
redshifts at greater distances -

in effect, further back in time -

could create a potted history

of how the expansion
of the universe was changing.

Astronomers were convinced
that gravity must have,

at the very least, been slowing
down the expansion.

The question was - by how much?

By plotting distance

against the redshift's
measure of expansion,

they could finally
answer that question.

Now, if you imagine the universe has
been expanding at the same rate -

the rate that it is now -
for its entire history,

I'd get a very simple line.

But astronomers knew
this couldn't be correct

because, of course, gravity is
putting the brakes on the expansion,

so the expansion of the universe
should be slowing down

and, if it's expanding
more slowly now,

it should've been expanding
more quickly in the past.

Space stretching more
would mean a bigger redshift.

Now, what does this mean
for our supernova?

Well, we know it was
eight billion light years away.

So we know it wouldn't fall
exactly on this line,

which corresponds to a redshift
of about 0.49.

It should sit maybe
somewhere over here.

Maybe at a redshift
greater than 0.5.

That means this line should really
be curving down like that.

But, of course, the exact shape
of this line would tell them

how much gravity is slowing down
the expansion of the universe

and that would tell them
the fate of the universe.

OK, so, David, you have
the spectrum ready now.

We have it.

Yes, bring it up.

And that gives you a measure
of the redshift.

So what did you measure that
to be here?

For this case, we measured 0.47.

0.47! Well, that puts it
on this side of the line.

That means it's not a larger
redshift, but a smaller redshift.

This is fascinating because
it's exactly what they saw.

Not redshifts that were larger,
but redshifts that were smaller.

And they saw this
time and time again

and it could only have
one explanation -

smaller redshifts meant that the
universe must have been expanding

more slowly in the past
than it is today.

In other words,
rather than slowing down,

the rate of expansion
of the universe is accelerating.

As more and more supernovae
were plotted,

the picture became clearer.

For the first few billion years
after the Big Bang,

it looked as if the expansion rates
had been slowing as expected...

..but then that changed

and the expansion
started to accelerate.

It's hard to stress how much
of a shock this was.

Back then, everyone knew that
the expansion of the universe

had to be slowing down.

Now, whether it would slow down
enough to stop and then recollapse,

that wasn't clear,
but it had to be slowing down.

After all, gravity had to be doing
its job of putting the brakes on,

but it wasn't.

About six billion years ago,

the expansion started to speed up.

Clearly, there was some
new and unexpected thing

going on in the universe -

something that science
didn't have an answer for,

something that was pushing
the expansion of the universe

at an accelerating rate.

It became known, for want of
another term, as dark energy.

The best estimates suggest
that dark energy

makes up 70% of the universe.

And that means the universe will not
collapse and end in a big crunch.

Instead, dark energy, not gravity,

will define the ultimate fate
of the universe.

Dark energy pushes
the universe apart.

It won't carry on expanding
steadily for ever.

Instead, dark energy forces
the universe to fly apart

at an ever-increasing rate.

Galaxies will become so far apart

that light wouldn't be able
to travel between them.

Each one will end up as an
individual island of stars

alone in the cosmos.

It may even become so extreme

that galaxies themselves
will be ripped apart,

leaving individual stars all alone
in the black emptiness.

Then again, maybe not.

After all, the effect of dark energy

seemed to suddenly appear between
six and seven billion years ago.

Who's to say how it'll behave
in the future?

That may sound bizarre

but, with the discovery of
dark energy, all bets are off.

It's hard to stress how little
we know about dark energy.

It has a name, but that's about it.

We don't know what it's made of,

why it's driving the universe apart

and, crucially, how it'll behave
in the future.

And that leaves a big hole in our
understanding of the universe

and its ultimate fate.

Dark energy may simply be part
of the universe,

built into the way it works...

..or it could point
to a fundamental problem

with the most important and trusted
scientific theories we have...

..ones that are at the very heart
of our understanding

of how the world works.

How the universe will end started
as astronomy's great challenge,

but the fate of the universe
has become

much more than just
an academic question.

Through the discovery of this
strange, enigmatic energy -

if, indeed, that's what it is - one
that defies current understanding,

it's spread to the heart
of fundamental physics.

Finding the answer to
how the universe will end

could have profound implications
on how we understand our world.

If you want to find out more about
the universe and the end of time,

go to the address below and follow
the links to the Open University.