Original subtitles

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.