How Big is the Universe? Horizon

The most ambitious map in history

is taking shape before our eyes.

And scientists are heading for the edge.

It may be the strangest map you'll ever see.

And it's bigger than you can believe.

It's a map of the entire universe.

There's this whole pattern to the universe we're starting to map out.

Seeing it really brought home the way the universe actually behaved,

in a way that all the numbers and equations never quite could.

Cosmologists are making sense of startling discoveries.

Medieval maps would say, "Here be monsters."

They weren't entirely wrong.

They're even building pictures of the invisible.

How do you map something that you can't even see?

Our brains build maps even where our telescopes cannot reach.

This is a map of everything we know.

And it's getting bigger every day.

It kind of hits you, how magnificent it is.

It's bigger than we can actually really even imagine.

The universe is so big,

we may never find the edge.

Mapping the universe is a job for pioneers.

Nick Risinger is blazing a trail through the American south west.

You have to be pretty persistent.

No stopping.

You've got to keep going.

Nick wants to put our entire galaxy on the map.

He's on a single-handed mission, to photograph the Milky Way.

New Mexico is a great place to take photos.

It's dry, it's high,

and there's not a whole lot of city around here.

There's a break in the weather,

and you get a full, almost a full night in.

Other times, you only get, you know, 10% of the night.

But it's all luck of the draw.

It's looking pretty good over there, actually.

In the modern world,

few of us have skies dark enough to see the Milky Way.

But Nick plans to show us our home galaxy

like we've never seen it before.

I'm trying to give people that broad, big-picture understanding

of the entire night sky, and where they fit into that.

Our galaxy has nearly half a trillion stars.

Most of them are too dim and distant to see.

But Nick's cameras

are more than 2,000 times more sensitive than the naked eye.

If I had known how much work it would be going into it,

I probably wouldn't have even started.

But my personality is, once you start something, you finish it.

After two years, he's photographed 20 million stars...

..by stitching together more than 37,000 separate images.

Some people might be driven crazy

by hearing shutters clack all night long.

But it's actually music to my ears, because it means they're working.

By combining data from six different cameras, he's captured

something that would tax even the world's most powerful telescopes.

His final image is the highest definition, true colour map

ever made of the Milky Way.

But he hasn't just mapped it...

..he's made a hand-held guide to the galaxy.

This is like a window to the sky.

And you can point it in any direction

and be shown exactly what you're looking at.

So here, we're looking at the centre of our galaxy.

This is our Milky Way.

You can see this bright cluster of many small stars.

The map reveals more features with every level of detail.

As we zoom in here to the centre of the galaxy,

I'll point out this dark patch here, this is the Pipe Nebula,

and it's one of my favourite landmarks to help me orient myself.

But it's the sheer size of the image that reveals its true ambition.

From one side to the other, it's 100,000 light years.

This image is such a big subject, and it makes you feel so small.

100,000 light years!

It boggles the mind just trying to comprehend just how vast that is.

But the fact is, the map of the universe has barely begun.

Anthony Aguirre, from the University of California in Santa Cruz,

is a theoretical cosmologist.

So he's used to thinking big.

Now to say that we're going to go out and make a map of the universe,

it almost sounds crazy. It sounds like real hubris, right?

"We're going to go and map the universe!"

And yet the universe, as it turns out, is really amenable to mapping.

But you have to think big, and clever.

And that's where the balloons come in.

Because the map of the universe isn't like other maps.

We have to think in a different way,

we can't just go out and look at the universe and draw things on paper

and say, "There's our map of the universe."

The universe is so big

that the laws of physics say we can't see all of it.

It's as if we're at the centre of a giant balloon, and we can't see out.

We can only see light. And light moves at a certain speed.

And so, as we look farther and farther away,

we're looking farther and farther back in time

because we're seeing light coming to us from long ago.

But there's only so far we can go back in time.

So there's only so far we can see.

It's called the "observable universe".

We can only map what's inside,

because the universe is only 13.7 billion years old.

There may well be a lot more universe outside,

but the light hasn't had time to reach us yet.

In the last 20 years, we've seen this tremendous expansion,

both in the amount and in the precision of knowledge that we have

about the observable universe.

This has allowed cosmologists to make a map of unbelievable scale.

The Milky Way could fit inside 10 million million million times.

Our entire galaxy's just a dot on the landscape.

In the observable universe,

there are 170 billion galaxies just like it.

Janna Levin is a professor of theoretical astrophysics.

She'd like to put every single galaxy we can see on the map.

But, before she can do that, it's vital to account for

one of the most surprising features of the universe.

Making a map of the whole universe

is not like mapping a map of the United States.

It's an observational fact that, if you look at the galaxies around us,

and the most distant galaxies that we can see,

they all appear to be moving away from us.

And, the further away they are, the faster they're moving away from us.

The galaxies aren't like landmarks on normal maps.

They don't stand still.

Everywhere we look, the most distant galaxies are moving away from us.

This a strange universe,

and the explanation is even stranger.

People want to imagine a central point

with everything exploding out from that point,

moving away only from that one central location.

That's really the wrong picture here.

That makes it sound like we're in a special place,

like somehow we're at the centre, and everything is moving away from us.

But actually it's not like that.

There's nothing special about our place in the universe.

If we went to another galaxy, we'd see exactly the same thing.

If you went to a distant galaxy,

they would have the same perspective.

They would look at all the galaxies around them

and see that they were moving away.

You really have to try to imagine

that every single point is moving away from every other point.

So no point is special.

No matter where you're standing in the universe,

if you look out, you will see galaxies moving away from you.

Think of it like cities on the map of America.

If you were standing in California,

you would see New York moving away from you.

But, from the perspective of New York,

you would see Boston move away.

And if you were standing in Chicago,

you would see New York and California moving away from you.

So, no matter where you're standing,

you see everything else moving away from you.

In the observable universe,

the galaxies are doing exactly the same thing.

The only explanation for that is that the space itself is stretching,

that the universe itself is getting bigger,

not that the galaxies are moving on the space,

but that the space is getting bigger.

It's as if the whole of America was getting bigger and bigger every day.

You'd think it would be impossible to keep the map up to date.

But cosmologists take everything into account,

by using careful measurements of the expansion rate.

It works like the scale factor on any road map.

Imagine the United States is doubling every day.

You wouldn't want to make a new map every day,

you wouldn't draw a new map.

All you would have to do really is change the legend.

Instead of one mile between tick marks,

the next day would be two miles, the next day would be four miles.

And that scale, changing on the side in your legend,

would completely account for the fact that the States kept doubling.

And so you could keep your originally drawn map.

The map of the observable universe doesn't change

except for the scale factor.

Right now, it's 46 billion light years to the edge.

But it's growing all the time.

So, while, at first, this is a little confusing,

trying to imagine something like a universe expanding,

we realise that, by drawing a simple map

and, by changing the scale on that map,

that we can handle the expansion actually quite simply.

For cosmologists, the expansion of the universe is not a problem.

In fact, it's a gift.

If space is stretching,

then the wavelength of light from the galaxies is stretching too.

The greater the distance, the redder the light.

This red shift effect

is the mapmaker's vital tool for measuring distance.

And red shift was the key to the next vital stage

in mapping the universe.

A survey to pinpoint the exact location of galaxies,

stretching 5.5 billion light years from Earth.

It started here, in one of the more unusual towns in America.

Welcome to Cloudcroft, New Mexico.

A place where you don't have to be an astronomer to map the universe.

Everyone in town can have a piece of the action.

To us, it's wonderful - I mean, it's just part of our everyday life.

On a clear night, my husband will say,

"Well, you're going to be busy tomorrow!"

Frances Cope has been working here for two-and-a-half years.

The last count, she'd mapped a quarter of a million galaxies.

It can be very therapeutic but mostly it's, to me personally,

it's a sense of fulfilment.

Tracey Naugle trained as a mechanic,

then retrained in galactic exploration.

It's neat that you are a part of discovering new galaxies,

it's kind of a good feeling.

Kristina Huehnerhoff is a freelance writer.

Mapping the universe helps her wind down.

It's very Zen, I think, because you're, you know,

you're putting things where they're supposed to be.

They all work with this man.

David Schlegel is a cosmologist

from the University of California at Berkeley.

When he first came to town,

the map of the universe was almost empty.

The only pictures we had of the full sky were on photographic plates,

images taken by Palomar Sky Survey in the 1950s.

And actually we were still using that in the 1990s,

that was the best picture that we had of the full sky.

The Palomar Survey was practically a museum piece -

photographed on fragile glass negatives.

Even by 1998,

only 30,000 galaxies had been placed on the map of the universe.

That's when David joined the Sloan Digital Sky Survey

at the nearby Apache Point Observatory.

We had the sense that it was going to be this great thing

that was starting, but it hadn't actually started yet.

What we wanted to do was something much more ambitious

and actually get a map of the million brightest galaxies on the sky.

The task required measuring the distance, and therefore red shift,

for every single one of these galaxies.

Obviously you need to look at more than one galaxy at a time,

so that's the trick.

If you were a futurist you'd say,

"Well, it's the 1990s, we have computers and we have robots."

The folks designing the Sloan, though,

decided to take the pragmatic approach

and say, well, we actually want this thing to work.

Instead of robots, the ingenious system they came up with

required a far more human touch.

And they would have to go round the universe

not once, but twice.

It's really doing two maps of the sky.

The first time round, they didn't measure any red shifts.

The telescope simply took photographs...

A map of the sky, but in two dimensions only.

It doesn't give the distance to each galaxy - yet.

We actually have from those images not very much idea

of where these things are in three dimensional space.

So at some level, it's just a pretty picture.

But the next stage was the trick.

They printed the pretty pictures in metal.

Each of these holes corresponds to our two dimensional location

of a galaxy on the sky, where if I look at this hole,

we have the longitude on this coordinate,

the latitude in this coordinate, and so the whole design

of this system is to as efficiently as possible get the light

from that one galaxy into that specific hole.

The plugging team from town connected every galaxy

with a fibre optic cable...

..then fitted the plate back over the telescope.

Second time around, the telescope measures the red shifts

for these specific galaxies alone.

1,000 galaxies on a plate,

nine plates a night

and one million galaxies in total

on a map crafted by human hands.

It's hard to wrap my head around the idea that we're looking at...

you know, with 1,000 fibres, we're looking at 1,000 galaxies,

and it's... I have a hard time wrapping my head around

that the universe is that big.

The Sloan Survey is one of the great achievements of Precision Cosmology.

Red shift measures the distance -

the third and final co-ordinate for every galaxy...

..to make a 3D Movie on a colossal scale.

Maybe you've seen things like this in the opening of Star Trek

or Star Wars or whatever, and that all looks great,

but it's not real.

This movie - it is the real Universe.

Every point of light on the map is a galaxy like the Milky Way.

Cosmologists can now see at a glance

how the galaxies are arranged in space.

What these maps let us do,

is it really allows us to test all the forces of nature we know about.

There is structure, really, on all scales.

The galaxies are not just placed at random -

they're bound together by gravity, in a vast cosmic web.

This goes on and on, and in fact up to the largest scales

that we can see. You can still trace these structures of galaxies.

But the most surprising discovery is what can't be seen.

Most of the universe is missing.

The gravity, due to the stuff that we see, due to say the galaxies

and stars, can't do the job.

It's simply not enough stuff to arrange things into the patterns

that we see, have galaxies spinning in the way that they do.

There's something else there. There's something beyond

the galaxies that we see, the visible matter.

There's some sort of Dark Matter out there.

Modern cosmology needs a new kind of map maker.

Because most of the universe is hiding in the dark.

We don't know what Dark Matter is

because it's never been detected on Earth.

We know it must be out there,

because its gravity is holding the cosmic web of galaxies together.

But we can't see it, because it doesn't give off light.

Someone has to find it and put it on the map.

British astronomer Richard Massey is a master of the invisible.

He's a member of a team hunting for Dark Matter,

based at the California Institute of Technology.

So, he's a frequent flyer to the city of Los Angeles.

When you're flying over America at night,

you see these criss-crossing lanes of street lights

spread out across the continent.

There's obviously some interesting stories going on down there,

in between these roads.

In fact, most of the story of what's going on in America

is actually happening in those empty spaces that you can't see.

Richard's task is like mapping those apparently empty spaces.

It's as if whole cities were hiding in the dark.

If we're driving across America, and trying to map out a new frontier,

we can see mountains and valleys

and streams and we can draw them all on a map.

But when we're trying to map out the universe,

most of its contents are invisible.

It takes imagination to find your way in a Dark Universe.

You have to dream up new ways to detect what can't be seen.

One possibility is that if Dark Matter doesn't give off light

maybe it absorbs light.

Ordinary matter, the stuff that we're made out of, casts a shadow -

because it absorbs light.

So we can see the ordinary matter in silhouette.

Unfortunately, Dark Matter doesn't give itself away that easily.

Light just goes straight through it.

Dark Matter doesn't interact with light in any way,

so we can't look for its silhouette to map out where it is.

We have to be a bit more ingenious about it.

The solution depends on a very simple idea.

It's like looking at lights in a swimming pool.

The secret to mapping Dark Matter that you can't see,

is to look at the light that you can see.

Everything that has mass, including Dark Matter,

actually bends the fabric of space and time that we're that we live in.

And if space is warped, then everything in it is distorted.

Even the paths of light rays.

The only way that Dark Matter might reveal itself is through gravity.

According to Einstein's Theory of Relativity,

all matter distorts space causing light to change direction.

The idea of General Relativity bending space and time

and deflecting rays of light sounds complicated.

But actually you see light rays bending all the time.

Look into a swimming pool and see your legs aren't in the right shape,

you know that there must be some water in the way.

The distortion of the lights depends on water ripples in the pool.

which in turn depend on where the swimmers are at any one moment.

Ah!

This is great, we're seeing these distorted images of lights

under the pool and by looking at the shapes of these, we can work out

what the ripples in the water are doing.

The survey team went looking for Dark Matter in exactly

the same way...

..with 1,000 hours of observations on the Hubble Space Telescope.

By looking at distant galaxies halfway across the universe,

by looking at their shapes

and the distorted images that we see of those,

we can work out what ripples there are in space between them and us.

And those ripples in space are caused by the Dark Matter.

The search zone was a thin column of the universe,

stretching eight billion light years from Earth.

The team were on the look-out

for distortions in the most distant galaxies.

Whenever you see galaxies

distorted into these strange uncharacteristic shapes,

you know that there must be something in between them and you,

something really massive, and even if it's invisible,

you can still map out where it is by the way it warps that space time.

The mapping technique revealed a ghostly, hidden universe.

The light from visible galaxies was recast in new and beautiful forms.

They've become these full rings,

distorted just like what are known as Einstein Rings,

whenever there's a big lump of Dark Matter in front of them.

The lumps become contours on a map of the invisible.

They reveal Dark Matter as the hidden iceberg

beneath the surface of the cosmic ocean.

What we're finding out there in the universe is really weird.

It's equivalent to the idea that only one out of six cities in America

actually has any people living in it.

The other five sixths of the population

are these invisible ghosts that we just can't see.

The survey has transformed the map of the universe.

It suggests that normal, visible matter

is just a fraction of what's out there.

In the search zone, Dark Matter outweighs it by six to one.

This is the stuff the universe is really made of.

For cosmologists, the road ahead has become a lot less certain.

Right now, we know the universe is expanding.

But given enough Dark Matter, it could have a different,

and very dark future.

It's sensible to conclude,

when we look at how that stuff affects the shape of space,

that the universe should be expanding but that it should be slowing down.

Dark Matter puts a very heavy foot on the brakes.

Because the more matter there is, the more gravity there is.

Gravity attracts. And so the cosmic expansion should be slowed down

by all that attraction.

If there's enough Dark Matter,

the universe will eventually stop expanding altogether...

..and go into reverse.

Gravity will bring everything back together,

in a final, cataclysmic big crunch.

The question is - when?

The search for the answer began here

on the Berkeley Campus of the University of California.

It's a distinctive outpost in the landscape of science

signposted with some of its greatest names.

There's even a car park reserved for Nobel Laureates.

Nine prize winners in a row - with five in Physics alone.

And it was here, in 1988, that Saul Perlmutter set out

to map the deceleration of the universe.

There's nothing you like more than a really good mystery.

I wondered if you could actually measure,

how much the universe was slowing down.

I thought it was a very exciting possibility that you could,

make a measurement, and find out what the fate of the universe was.

Saul was the leading light

behind an international team of physicists and astronomers.

Under his guidance, they embarked on a ten year voyage of exploration

far across the observable universe.

The key was to measure how fast the universe was expanding

in the past, compared to now. They planned to map ancient galaxies -

10.8 billion light years from Earth.

But it would take a whole decade to find and analyse

what they were looking for.

A candle.

If you want to measure distances across the universe

you would like to be able to use an object that's of known brightness.

We call anything that we know the brightness of a Standard Candle.

A Standard Candle always has the same brightness -

so you can use it to measure distance very precisely.

The further away it is,

the dimmer it will appear in our telescopes.

But candles are elusive objects.

We hunt, for what astronomical object could you possibly use,

that will behave in this very regular way,

so that you can actually compare the distances.

The galaxies themselves are no good.

They come in many different shapes and sizes

and at this distance, they're so dim we can barely see them.

We're talking about distances that are even more vast than usual

for astronomy. Now we need to look at some of the most distant objects

in the universe so these had to be very bright objects.

Saul had a very bright idea.

He would find his way by the light of a dying star.

A supernova.

When one of these supernovas explode,

that one star can be as bright as the entire galaxy

of a hundred billion other stars.

So this is a remarkably bright, single event.

Saul had a special kind of supernova in mind.

A Type 1A is triggered

when a dying star draws in mass from its neighbour.

Just at the point where there's a critical mass,

there will be a runaway thermonuclear explosion.

So that means that it's triggered at the same mass every time.

Same mass every time means same brightness every time.

They're perfect standard candles.

But Saul had to find them first.

If you could work with anything else in the world

besides a supernova to do your research you would.

They're just a real pain in the neck to work with.

They're rare, they're random and they're rapid.

A supernova only burns brightly for three weeks.

And in any given galaxy, they explode without warning

roughly once every 300 years.

With those odds, you can't book valuable time

on the world's best telescopes.

It makes a terrible proposal, if you were to say that,

"Sometime in the next several hundred years,

"a Type 1a supernova, might explode, somewhere in this galaxy.

"I would like the night of March the 3rd, just in case."

But Saul had a plan to get the odds working in his favour.

With billions of galaxies in the observable universe -

there are dozens of supernovae every night.

Saul's team spent six years

perfecting a new system for supernovae on demand.

They took snapshots of thousands of galaxies at once,

then repeated them two and a half weeks later.

First you don't see a supernova.

Now you do.

That's very important, that two and a half weeks,

because that guarantees, that everything you find, that's brighter,

on the second night than the first, is on the way up.

We can now guarantee that there would not just be one

Type 1A supernova, but there would be a half dozen.

Saul now knew exactly where to point

one of the world's most powerful telescopes -

the Keck Observatory in Hawaii.

He was finally ready to measure the deceleration of the universe.

But by late in 1997,

the team was getting some very weird results.

The points were not showing up where you would expect.

This was exciting.

The supernovae distance measurements

didn't match the predicted deceleration.

We were then faced with the question,

"OK, what else could be going wrong?"

Saul and his team spent five more anxious months,

eliminating all possible sources of error.

But by January 1998 they were finally ready to go public.

The more we checked, the more we,

fine tuned every little step of the calibration,

the more the weird result didn't go away.

The weird result has reverberated through

the world of science ever since.

In January 2012,

Saul Perlmutter won the Nobel Prize for Physics

and booked a parking space for life.

At the end, we concluded that actually, the universe really isn't slowing down,

it's actually speeding up in its expansion.

And that was a big shock.

It's been described as one of the biggest shocks in modern cosmology.

This is a Runaway Universe

and everyone's on board -

whether we like it or not.

We find out that the universe is not just expanding,

but that it's getting faster and faster.

The cosmological community, when this result came out,

was completely incredulous.

I didn't believe it when I first heard about it.

I don't even think I paid very much attention to it at the time.

We know the universe doesn't look like this.

There had to be something wrong with these observations.

I thought they would go away, I really did.

Of course, I was wrong.

It's sometimes really fun to be wrong.

Welcome to a very new picture of the universe.

But even the experts can hardly believe it's real.

The most famous force in physics has met its match -

because the entire universe is defying gravity.

This was saying that there was something

that fills the universe, and causes an anti-gravity force.

Something that was causing everything to push everything else apart,

and to make the universe bigger and bigger

in an accelerated way.

Gravity acts as a brake -

pulling back on the expansion of the universe.

But we now know there's another, more mysterious force -

with its foot on the gas.

What's doing the pushing? What's that force that's forcing everything apart?

Well, we don't know, but we did work out what to call it.

We have a name for it. We call it dark energy.

Cosmologists don't know what dark energy is.

They only know what it does.

Where gravity pulls -

dark energy pushes.

You don't see this stuff.

You don't see it doing anything, directly.

Basically, it's sort of this one hit wonder,

that just does one thing, it causes an anti-gravity force.

We don't have any other handle on it.

Dark energy is dark matter's dark adversary.

A shadow on the entire universe.

There's dark energy in the galaxy.

There's dark energy, here on Earth.

There's dark energy passing through us right now. We're filled with this dark energy.

We don't see it - we don't feel it.

But it's everywhere.

It's kind of just a uniform colouration to our map.

73% of the universe is dark energy,

but you'd never know.

In everyday life, this stuff is just hard to detect.

Now, it's true that between my two fingers,

there's an anti-gravity force, right now.

But that anti-gravity force is so incredibly minuscule,

that I'll never ever notice it.

It's only when you get to really large scales,

that you really see the affect of this stuff.

If I could move my fingers, all the way across the universe,

then they'd feel this tremendous push apart, due to this dark energy.

In the really big scheme of things,

dark matter is fighting a losing battle...

..because there's only so much of it to go round.

If you add more space,

if you give more place for those little pieces of matter to be,

then, the density of them goes down.

You just see less of it - it gets diluted.

As the universe expands, dark matter thins out

until it can no longer compete with dark energy.

The really crucial thing about how this dark energy behaves,

is that it doesn't dilute.

When the universe doubles in size,

you've got twice as much dark energy.

You make it four times as big, you've just got four times as much dark energy.

Once you get to this cosmological scale,

the biggest possible scale, it becomes the biggest game in town.

It becomes the prime player.

Dark energy is on the map.

But cosmologists can't explain it.

Depressing, or exciting? I think it's exciting.

As a map maker, this is a strange thing.

We go out, we make this map, we discover this land,

we've mapped it out, and we still don't know what it is.

I love that.

The entire observable universe is saturated in dark energy.

But there's one final set of clues to be found - on its furthest edge.

And it may contain the secrets to the universe beyond.

We're heading off the map into impossible territory.

The edge of the observable universe

is the furthest horizon our telescopes can see.

But for cosmologists like Sean Carroll, that's not enough.

He wants to know the size of the whole universe.

I definitely think it's OK to think about parts of the universe that we can't observe and can never observe.

We've done a very good job at understanding

what the universe looks like in that visible portion.

So now when our imaginations roam,

they often sneak outside the visible portion to ask what might

the universe look like beyond our visible horizon.

The universe that we can't see -

that's the playground for theorists now.

But if we can't see the rest of the universe,

how can we figure out how big it is?

For Janna Levin, it's a similar task to working out the shape

and size of the earth.

But there's a catch.

We know we could step far from the Earth, as an astronaut has.

We can look down on it

and see from the outside that it was a sphere and it was curved.

You can't step outside of the universe.

You have to do everything from inside of space.

Without leaving the earth, how do you know it's round,

and therefore has finite size?

It could be completely flat,

and stretch to infinity in all directions.

One way is to use a simple piece of mathematics.

All you have to do is draw a triangle.

If you're drawing a small enough triangle on the beach,

you won't notice the curvature of the earth.

It will look like a normal triangle, you'll be able to draw the lines pretty straight

and the interior angles will look like they add up to 180 degrees,

it will look like the triangle you draw on a flat sheet of paper.

But this isn't a normal triangle,

because the earth's surface is curved.

It's just so subtle,

that the sides of the triangles still look straight.

It would probably be a challenge on the beach to draw it big enough

that you would be able to notice the curvature of the earth.

The key is to make the curvature more obvious -

by drawing the biggest triangle you can.

If I draw a triangle big enough that it comes from the North Pole

and it wraps all the way around North America,

now it's very obvious that those angles are bigger than 180 degrees

and that the sides of the triangle are not straight lines.

So, we can show the earth is curved

and therefore has finite size without leaving it.

And we can find out the shape and size of the universe

in exactly the same way -

by looking for triangles of light.

Light will travel in a straight line if the space is flat,

and light itself will travel in an arc if the space is curved.

These curves are going to be so subtle,

more subtle than the curvature of the earth.

We really have to look back

as far as we possibly can.

And that means the oldest relic we have in the universe.

So that means looking at things

like the light left over from the Big Bang.

The early universe was a hot, dense fireball.

When it cooled, a pattern of light emerged

at what is now the edge of the observable universe.

This is the cosmic microwave background.

The CMB was discovered in the 1960s.

But throughout his career, Sean Carroll

has been able to explore it in greater and greater detail -

waiting for triangles to emerge.

It takes good technology to do it,

you need better and better receivers,

less and less noise in your detector,

and ultimately you need satellites

to get a really good 360 degree view

of the whole cosmic microwave background.

It was NASA's WMAP mission in 2003

that brought the most vital contours into sharp focus.

WMAP for the first time had that resolution

so when WMAP came out, we could really use those features

to make a big triangle and measure the geometry of space.

Continents begin to appear, smaller islands,

you get a finer resolution of the coastlines and so forth.

The islands are miniscule temperature variations

in the early universe - less than 100,000th of a degree...

..a distinctive feature for making triangles.

These splotches we see in the microwave background appear at all different sizes

but there is a best size for them to be,

there's a size at which the fluctuations are the strongest.

We know how big they are, we know how far away they are,

so between us and the size of a feature in the CMB,

we can measure a triangle and use that to infer the geometry of space.

The earth, plus the opposite sides of the island,

form the three points of a very long, thin triangle -

The key to measuring whether the universe is flat or curved.

If the universe were positively curved,

if the angles inside the triangle added up to greater

than 180 degrees, then it would be finite in size.

If the spatial geometry is flat,

if the angles inside the triangle add up to 180,

then it could go on for ever.

The result is one of the greatest triumphs of modern cosmology.

A miracle of precision map making

that measures the angles of the triangle to the third decimal place.

And it says that the universe is infinite.

The answer is that Euclid was right,

space seems to us to be flat as far as we can measure it.

That means that the simplest picture of the universe,

is a universe that's infinite.

We really could live in a universe where,

there's galaxy after galaxy after galaxy, in every direction.

Up, down, sideways. And, it never stops.

Cosmologists have found a way

to picture the universe in its entirety -

confirmation of the tremendous power of making maps.

It will never cease to amaze me -

we human beings here on this tiny little rock are able to reach out

with our instruments and our brains

to understand the whole shebang.

And if an infinite universe isn't big enough for you -

then Saul Perlmutter has proved it's still growing.

All the distances are getting bigger, every day.

So, it's still infinite, all the same galaxies are there,

it's just that we have pumped more space

between every point in this infinite universe.

That's really mind boggling.

But even this isn't the end of the story.

There may be one final, bizarre twist in the road.

Because Anthony Aguirre thinks our universe may not be alone.

Sometimes when I'm headed down the highway and I'm driving,

you know, my wife will say,

"Anthony, you're going 40 on the highway."

And then she knows that I'm thinking about other universes.

He thinks there may be other universes

because of the process that created our own.

It's called inflation.

It describes an exponential expansion

in the moments after the Big Bang,

at a speed the universe would never repeat again.

Inflation has been a very successful theory in predicting

observed properties of our universe

and how our observed universe came into being.

Inflation may have started out as a mathematical theory...

..but it has gained acceptance after successful testing

against the evidence from the cosmic microwave background.

I was amazed when I saw the results come in from those satellites

that reproduced all the bumps and wiggles

and all the detailed properties of that microwave background

that inflation had predicted.

Inflation explains how the observable universe developed.

It was doubling in size over and over again in a tiny fraction of a second,

going from something like a billionth of the size of a proton

to something maybe the size of a bubble, a soap bubble.

But inflation didn't stop with our own universe.

Anthony believes it may have happened over and over again.

This is really a side effect.

It's a huge side effect, it's an amazing side effect,

but it's a side effect of something we invented already for a different purpose.

It's a process called eternal inflation.

There could be as many as we can imagine.

Anthony's vision - of an infinite number of infinite universes -

may sound far-fetched.

But the search is on to find evidence to support it.

Evidence from the oldest part of our map.

Every once in a while we could have sort of a cosmic collision

with another bubble.

It would leave an impact, it would leave a bruise,

a disc in the sky

on the microwave background radiation that we could look for.

Anthony and his colleagues have simulated

what a collision of universes would look like.

A dark bruise, superimposed on the cosmic microwave background.

He doesn't yet have enough data to test it,

but it's a tantalising glimpse of what the map could reveal

with the next generation of satellites.

In principle I think this scenario with all these bubbles

is testable, we can actually go out and look for them.

This may be the ultimate map of the universe.

We're talking about understanding and testing and theorising

in a scientific way about an infinite number of universes.

It's simultaneously so mind-boggling

and yet it's still rigorous science -

we can do mathematics, we can do experiments, we can really test it.

Some day we'll understand the universe so well

that we can literally take that map, put it on a little compact disc

and put it in our pockets and take it home.

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