All language subtitles for PBS.NOVA.Wonders.Series.1.Part.6.Whats.the.Universe.Made.Of.720p.HDTV.x264.AAC.MVGroup.org.eng

o you wonderer about?

MAN:
The unknown.

What our place
in the universe is.

Artificial intelligence.

Hello.

Look at this,
what's this?

Animals.

An egg.

Your brain.

RANA EL KALIOUBY:
Life on a faraway planet.

WILLIAMS:
"NOVA Wonders"-- investigating
the biggest mysteries.

We have no idea
what's going on there.

These planets in the middle

we think are
in the habitable zone.

WILLIAMS:
And making incredible
discoveries.

WOMAN:
Trying to understand

their behavior, their life,
everything that goes on here.

MAN:
Building an artificial
intelligence

is going to be the crowning
achievement of humanity.

WILLIAMS:
We're three scientists

exploring the frontiers
of human knowledge.

ANDRÉ FENTON:
I'm a neuroscientist

and I study
the biology of memory.

EL KALIOUBY:
I'm a computer scientist

and I build technology

that can read human emotions.

WILLIAMS:
And I'm a mathematician,

using big data to understand
our modern world.

And we're tackling
the biggest questions...

Dark energy?
ALL: Dark energy?

WILLIAMS:
Of life...

DAVID PRIDE:
There's all of these microbes,

and we just don't know
what they are.

WILLIAMS:
And the cosmos.

♪ ♪

WILLIAMS:
On this episode...

ALEX FILIPPENKO:
Hey, it's there!

We got something!

WOMAN:
The first-- ever.

WILLIAMS:
The hunt for the secret
ingredients of the universe.

FLIP TANEDO:
This was a mystery.

SAUL PERLMUTTER:
We came up with
this bizarre result.

DAVID KAISER:
Most of what astronomers
had assumed about our universe

fell apart.

(explosion)

WILLIAMS:
The mysterious,
invisible forces

that control the fate
of the cosmos.

FILIPPENKO:
It's 70%

of the contents of the universe.

MARCELLE SAURES-SANTOS:
We have no idea what it is.

Very weird!
I mean, it's crazyland!

WILLIAMS:
"NOVA Wonders"--

"What's the Universe Made of?"

Right now.

WILLIAMS:
When you stare up at the sky
at night,

it's hard not to wonder,
what's out there in the cosmos?

Today we can see
incredible things.

Telescopes gaze at galaxies
far, far away.

And we've peered back in time

almost to the beginning
of the universe itself.

But in recent years, astronomers
made a disturbing discovery:

our universe
is hiding something.

Actually it's hiding a lot.

EL KALIOUBY:
It turns out,
all the stuff we can see,

all that we've come
to understand,

adds up to only
5% of the universe.

The other 95% is made up
of two mysterious ingredients.

Dark matter and dark energy.

Not only do they make up
most of the cosmos,

but the two are in
an epic battle

to control the fate
of the universe.

(explosion)

FENTON:
Today, scientists are on
the hunt,

trying to understand
these dark mysteries.

WILLIAMS:
Uncovering new secrets

about the history
of our universe

and predicting
a shocking future.

I'm André Fenton.

I'm Rana El Kaliouby.

I'm Talithia Williams.

And on this episode,
"NOVA Wonders"--

"What's the Universe Made of?"

♪ ♪

♪ ♪

(phone vibrating)

I think it was 7:40
in the morning,

my phone rings,
and my colleague says,

"Wake up!"

♪ ♪

WILLIAMS:
Early on an August morning,

at her apartment in Chicago,

Marcelle Soares-Santos

gets the call she and dozens
of other astrophysicists

have been waiting for.

SOARES-SANTOS:
My colleague says,
"We received a signal.

We have to take action."

And I'm like, "Oh!

This-this is really happening."

♪ ♪

WILLIAMS:
The signal is of vibrations
created by a gigantic explosion

across the cosmos.

We are talking about
two neutron stars.

WILLIAMS:
130 million light years away,
two massive neutron stars

have violently crashed together.

SOARES-SANTOS:
Very dense objects
colliding at approximately

the speed of light.

(explosion)

The explosion is gigantic,
it's tremendous.

WILLIAMS:
Astronomers around the globe
rush to their telescopes,

hoping to capture
the faint light

of this distant catastrophe.

On a mountaintop in Chile,

some of Marcelle's colleagues
point a powerful telescope

toward a patch of sky
in the constellation Hydra.

SOARES-SANTOS:
We expect the light
from these sources

to fade away quickly,
so you have to act fast.

♪ ♪

WOMAN:
The data taking has started.

WILLIAMS:
As the pictures come in,

researchers all over the world
sift through the data

looking for one
extraordinary dot.

The sky is full of beautiful,
bright sources,

but there will be one
that was not there before

that is there now.

WILLIAMS:
Finally...

Holy (bleep),
look at that.

WILLIAMS:
...someone spots something.

That blob here.

WILLIAMS:
Very low on the horizon,
there's a light in the sky...

We found it!

WILLIAMS:
...that has never been seen
before.

MAN:
That really small
spot of light.

MAN 2:
That one, right there.

Very, very cool.

It's spectacular!

You don't get many chances
like that.
Yeah.

Looking at the screen,
and you're like,

"Is this really happening?

Is this real?"

(explosion)

♪ ♪

WILLIAMS:
This tiny blob is the light
from that titanic collision

in a galaxy far away.

♪ ♪

Not only is this the first time
such an event has been captured,

but for Marcelle
and her colleagues,

this kind of data
could help solve a mystery

that's perplexed astronomers
for years--

to decipher the strange,
invisible ingredients

that make up the vast majority
of our universe.

♪ ♪

But the clues
to solve this mystery

aren't just in galaxies
deep in space...

They could be all around us.

In a remote Canadian forest
just north of Lake Huron,

another group of scientists
is setting a trap.

But their snare is not aimed
at the sky...

(metal rattling, radio chatter)

...it lies in
the other direction.

Deep beneath the forest is
the Vale nickel and copper mine.

(metal clanging)

KEN CLARK:
So we're about 6,800 feet
underground.

♪ ♪

WILLIAMS:
For more than a century,

miners here have pulled
metal ore

out from the surrounding rock,

but now another team has come.

CLARK:
We're down here in this mine,

because it shields out
all the radiation

that would make our detectors
unusable on surface.

WILLIAMS:
Ken Clark is a different
kind of miner,

seeking a treasure
far more precious.

(metal clanging,
machinery humming)

That noise
is the ventilation doors,

it effectively creates
an airlock.

♪ ♪

WILLIAMS:
These machines are designed to
detect a very elusive particle.

CLARK:
It doesn't interact with light,
we can't see it.

But the discovery really could
be just around the corner.

♪ ♪

WILLIAMS:
Ken is one of dozens
of scientists here

hunting a substance
so mysterious

it doesn't even have a name.

They call it dark matter.

CLARK:
There's a lot of experiments,

we're all kind of racing
to try and find this thing.

♪ ♪

WILLIAMS:
Racing to find it,
because scientists believe

this mysterious stuff
played a key role

in shaping the universe
as we know it.

Ken and Marcelle are just two

in a long line
of cosmic detectives

trying to understand
how our universe works

and what it's made of.

It's an investigation
that's revealed

bigger and bigger surprises,

starting about
a hundred years ago.

Back then, most scientists--
even Albert Einstein--

thought that the entire universe
consisted only of this--

a single galaxy, the Milky Way,
sitting in space.

But this small, simple universe

was about to be blown
to smithereens.

(explosion)

The telescopes back then
were small, but besides stars,

they could make out
faint glowing clouds,

which scientists believed
were made of gas and dust.

They called them nebulae.

One scientist, Edwin Hubble,
decided to take a closer look.

PRIYAMVADA NATARAJAN:
What Hubble needed to do

was to actually measure
the distance to these nebulae.

WILLIAMS:
Using one of the most powerful
telescopes of the day,

Hubble was able to pick out

stars in these nebulae
and calculate their distances.

To his amazement, he found that
they were over four times

farther away from us
than any star seen before

in our Milky Way.

KAISER:
The distances from us
were truly astronomical.

These nebulae,

they weren't just smears of gas,
they were indeed

collection of stars
all their own

outside of our galaxy.

WILLIAMS:
Hubble realized that this
nebula-- known as Andromeda--

wasn't a cloud of gas at all,
it was another galaxy.

And it wasn't the only one.

♪ ♪

KAISER:
We learned that
the Milky Way Galaxy

is one of a vast sea
of galaxies,

hundreds of billions--
maybe more!

Galaxy, after galaxy,
after galaxy

in every direction--
down, up, sideways,

in an infinite universe.

WILLIAMS:
What's more, Hubble,
along with other astronomers,

could see these galaxies
were on the move,

rapidly flying away from us.

Hubble found that the universe
isn't static after all.

It's expanding.

KAISER:
Most of what astronomers
had assumed about our universe

fell apart.

KATHERINE FREESE:
It was a complete
paradigm shift,

it was a complete shock
to everybody.

Pretty disorienting.

WILLIAMS:
Far from being confined

to a single galaxy--
the Milky Way--

the universe
was filled with galaxies,

and they were all on the move.

Hubble's discovery means
that the universe is big--

and getting bigger
all the time--

with galaxies flying away
from each other.

But if that's true,
if everything in the universe

is flying apart right now,
what did it do in the past?

What would happen

if you ran the clock backwards?

(button clicks,
stopwatch ticking)

TANEDO:
Essentially,
what we're doing,

is we're playing the tape
backwards,

and we're saying,

"If the universe
is getting bigger now

"it must have been
small earlier.

It must have been really,
really small a long time ago."

(ticking)

WILLIAMS:
Keep rewinding, and everything
gets closer and closer together.

Eventually, they get so dense
that you have a soup

of elementary particles.

All the stuff we see around us

was compacted to literally
a single point.

All of space
was a little tiny dot.

♪ ♪

WILLIAMS:
This is how it all started.

We don't necessarily know
why it started that way,

but it started out
as this very, very small region

of high density.

(clicks, explosion)

WILLIAMS:
The Big Bang.

(ticking)

As the clock ticks forward now,

in the very first fraction
of a fraction of a second,

scientists think the universe

went through an intense period
of expansion.

We call that era
Cosmic Inflation.

BRIAN NORD:
The initial stages
are like a growth spurt.

So there's this period
of inflation,

where the universe's size
grew really, really fast.

Ripping apart at an enormous,
enormous, exponential rate.

(explosion)

WILLIAMS:
As it cools,
the growing universe condenses

into a soup of exotic particles.

The universe is a hot, dense,
plasma.

It's a hot gas.

There's particles,
there's anti-particles.

They're coming in and out
of existence.

WILLIAMS:
The seconds tick by,

the soup of particles
remains unsettled.

380,000 years pass by.

As the universe keeps expanding,
it cools.

MELISSA FRANKLIN:
Then you get atoms, because
things are cooling enough

that atoms can actually form

where you have protons
and neutrons

in the center,
and electrons around them.

KAISER:
For the first time
in cosmic history,

the temperature falls
just low enough,

and that changes things forever.

(explosion)

WILLIAMS:
Finally,
light can travel across space.

This is a snapshot
of that moment--

a baby picture of the universe.

An image of the universe
when it was just an infant.

380,000 years
after the Big Bang.

Now that may sound like a
long time on a human time scale,

but compared with the age
of the universe,

13.8 billion years,

it's just an instant
near the very beginning.

WILLIAMS:
Already, the blue areas reveal

where matter
will clump together,

forming the seeds that will grow
into galaxies.

The first stars are born,
and die,

and re-form
in a cycle generating

the building blocks for planets,

ever more complex chemistry,
and, eventually, us.

♪ ♪

But why did galaxies begin
to form at all?

The energy that was expanding
the universe

ever since the Big Bang
should have spread

the little bits of matter
too thin.

So as the universe
continues to expand,

we might have expected
these little tiny lumps

in the universe to really get
smoothed out.

Instead, we know the opposite
happened.

♪ ♪

WILLIAMS:
How could so much of the matter
clump together

to form the major structures
of the universe?

It's a question that's plagued
astronomers for decades.

♪ ♪

The first clue came from a Swiss
astronomer named Fritz Zwicky,

just a few years
after the discoveries

that had suggested the Big Bang.

Zwicky noticed that these
newly discovered galaxies

were behaving oddly.

FILIPPENKO:
Fritz Zwicky looked at
clusters of galaxies

and found that the individual
galaxies within those clusters

are moving so fast, that
the clusters should fly apart.

Moving around so rapidly,

that it was impossible
to understand

why they didn't just
wander away.

Something clearly held them
in these orbits.

WILLIAMS:
Zwicky could see nothing
in his telescope to explain it,

so he called the phenomenon
"dunkle materie,"

translated as "dark matter,"

and then the idea
promptly faded away.

Zwicky's observation might have
ended up forgotten.

And for nearly 40 years, it was.

Until an astronomer named
Vera Rubin entered the field.

TANEDO:
Vera Rubin was one of these
astronomers

who was not appreciated
until much later.

She was a woman in astronomy
at a time when the field

was not particularly friendly
to women.

Rubin chose to work
in a relatively quiet area

of astronomy,

making straightforward
measurements of stars

as they orbited
in their galaxies.

Here's what we get.

WILLIAMS:
But she too noticed

something bizarre happening.

The stars way out here
are going very fast.

WILLIAMS:
The stars at the edge
of the galaxies

were moving so fast

that they should have been
flung off into space.

TANEDO:
This was a mystery

that these stars were moving
too fast

to be explained by
ordinary matter.

♪ ♪

Think about a spinning wheel,

covered in water.

If the wheel is moving slowly,
the water clings to the wheel.

But spin it fast enough...

♪ ♪

The water flies off.

The same thing should happen
out in the universe.

Stars swirling around
in a galaxy--

if they orbit too fast,
they'll get flung off,

out into space.

Except that's not what
Vera Rubin sees.

WILLIAMS:
The galaxies are spinning fast,

but the stars stay
in their orbits.

What's holding them there?

It has to be gravity.

...response,
gravitational pull

from something
that's not bright.

And we don't know
what that is.

♪ ♪

WILLIAMS:
But gravity doesn't exist alone,
it depends on stuff--

matter and energy.

Vera Rubin knew that gravity
is produced by mass.

Einstein had proven it.

KAISER:
The main takeaway message

of Einstein's
general theory of relativity

is that gravity is nothing but
the warping of space and time.

Space-time itself becomes
something like a fabric

that when we put objects
like galaxies

within this fabric of
space-time, it will warp.

WILLIAMS:
Massive objects create hills and
valleys in the fabric of space,

and these create gravity.

The one thing that we know,

is that if you have
stuff with mass,

stuff with energy,

it's going to pull planets.

It's going to pull stars.

It's going to pull
other galaxies.

WILLIAMS:
The amount of gravity all
depends on the amount of mass.

The more stuff rolling around
in the fabric of space,

the more distortion,
the more gravity.

It was clear to Vera Rubin
that a lot of gravity

was holding the stars in place,

but there wasn't enough stuff--

enough visible matter--
to generate so much gravity.

There must be
some missing matter.

♪ ♪

Dark matter was real.

♪ ♪

It doesn't shine,
it doesn't give off light.

By definition it is the stuff
that we have a really hard time

being able to quantify.

That's why they called it
dark matter.

The more astronomers looked,

the more dark matter
there seemed to be.

But how much is there?

And where exactly is
all this mysterious stuff?

♪ ♪

Astrophysicist Priya Natarajan
is trying to find out.

NATARAJAN:
I have worked my entire career

on trying to understand
the nature of dark matter.

♪ ♪

WILLIAMS:
But how do you understand
what you can't see?

Luckily, this invisible
dark matter gives itself away

because it has a habit
of playing tricks with light.

(beeping)

NATARAJAN:
In 2014,
with the Hubble Space Telescope,

a very intriguing kind of object
was observed.

WILLIAMS:
It appeared to be a galaxy
with four exploding stars,

called supernovae,
going off at the same time.

Like four evenly-spaced
supernovae.

WILLIAMS:
In reality,
there's only one supernova.

But it somehow shows up
in four different places.

What's going on?

This configuration of four
evenly-spaced multiple images

is called an Einstein Cross.

It was predicted by Einstein.

In reality,
one supernova went, "Whoop,"

and we had a little gift.

♪ ♪

The paths of light rays
are bent into a configuration

with four distinct images
of the same supernova.

WILLIAMS:
Somehow the light
from that one supernova

traveled along
several bending pathways,

arriving at four different spots
in the sky.

NATARAJAN:
The phenomenon of light bending

is something
we actually encounter every day

and it's all around us.

So, for example,

if you look at,
say, graph paper

through the bottom
of a wine glass,

you know this is
a regularly spaced grid,

but because of
the light bending,

you can actually see a
stretching of the grid pattern.

WILLIAMS:
In the cosmos,
what bends light is gravity

distorting the fabric of space.

It's called
gravitational lensing,

and it can produce
spectacular results--

smears, rings, smiley faces.

It can even make
a supernova show up

in four different places
at once.

For Priya, these aren't
just fascinating illusions.

They are crucial clues
in the dark matter mystery.

Since gravity is what bends
the light in these images,

and dark matter creates gravity,

the distortions can reveal where
dark matter is in the universe.

NATARAJAN:
And so it's the dark matter

that is producing this
huge amount of distortion.

WILLIAMS:
So Priya is gathering a giant
database of these distortions,

all in her quest to map out dark
matter throughout the universe.

(beeping)

And Priya and maps?

Well, they go a long way back.

NATARAJAN:
We're going
to one of my favorite places,

where I fulfill
all of my childhood fantasies.

The map room at the
Beinecke Rare Book Library.

WILLIAMS:
Priya's quest grew from
an obsession

that's gripped her
since she was a young girl.

I was obsessed with
all kinds of maps and atlases

when I was young.

I'm-I'm....
like, I'm crazy about maps.

♪ ♪

It's beautiful.

♪ ♪

These mappers of yore,

when they ran out of data
or knowledge,

it was marked
as "terra incognita"--

mythical places
that await exploration.

WILLIAMS:
The places that young Priya
most wanted to map

were not on earth,
but in the heavens.

There was something
about the cosmos

being a little bit out of reach

that really attracted me.

WILLIAMS:
As soon as she got
her first computer,

she used it to create
a star chart.

It was a hard problem,

and I sat down for six weeks,

and I wrote the program.

♪ ♪

These were not things

that no one had figured out
before, right?

But I was figuring them out

for the first time.
I was hooked.

♪ ♪

WILLIAMS:
Today, Priya is fulfilling
her dream of exploring

the frontiers of the universe.

She's one of several researchers
writing computer programs

that use gravitational lensing

to map the location
of dark matter.

This is one of the largest maps
of dark matter.

(computer mouse clicks)

The red regions are where you
have an excess of dark matter.

If we zoom into
a dark matter simulation,

it looks rather like
these fibers,

almost like neurons.

WILLIAMS:
Using computer simulations

of the early universe,

astronomers now think that
dark matter formed a giant web.

Where the dark matter filaments
cross, at these nodes,

you form these clusters
of galaxies.

WILLIAMS:
Astrophysicists now realize
dark matter must have played

a central role early on,
drawing together ordinary matter

and allowing galaxies to form.

We wouldn't be here
if it weren't for

the powerful pull
of dark matter.

NATARAJAN:
Our current understanding
of dark matter is

literally it shapes the universe
that we see.

WILLIAMS:
And what's clear--
there's a ton of it.

By now we actually have
many independent measures,

many independent ways
to estimate

the total amount of dark matter

in the universe.

And, amazingly, each of them
points to an amount

of something like five or five
to six times more dark matter

than ordinary matter.

For every atom
of ordinary matter,

there seems to be

five times more mass
in some mysterious dark matter

throughout the entire universe.

Let's say I'm made
of ordinary matter,

the stuff we see and understand,
like atoms.

Now add dark matter,

and it's as if
for every one of me,

the universe has about
five more,

made of entirely different
stuff.

They're there,
but completely invisible.

We only know they exist
because of their gravity.

It seems totally bizarre
and kind of freaky,

yet that's what the universe
is telling us.

The vast majority of matter
is this mysterious stuff,

dark matter.

But what is it?

I can't imagine that dark matter
is fire-breathing dragons

that will come out
of black holes to eat us.

It's definitely not that.

But could it be
a heavy particle?

Could it be a light particle?

Can it do exotic things?

Maybe it's something
really boring.

I don't know.

WILLIAMS:
These kinds of questions
are nothing new.

People have been wondering
about what exactly matter is

for millennia.

But only recently
have we had the tools

to actually figure it out.

A hundred years ago, in a sense,
all matter was dark matter,

because we didn't have
the technology to pull apart

what these particles are
that everything is made out of.

WILLIAMS:
In the early 20th century,

while Hubble was peering up
at the cosmos,

other scientists were focused on
the tiny world of atoms,

trying to decipher the nature
of matter itself.

They devised enormous machines,

called accelerators,

to break atoms
into their constituent parts.

♪ ♪

Accelerators revealed a zoo
of elementary particles

with all sorts of
whimsical names.

LYKKEN:
Particle names,
some of them are cute,

like neutrino, which I think
is one of the best names.

Quarks.

You have up and down quarks.

Top quark.
Bottom quark.

Charmed and strange quarks,
and truth and...

Beauty quark.

Gluino.
Electron.

Photino.
Photons.

Gluons.
Pion.

Kaons.
Upsilons.

The Higgs-Boson.
Oh, positron actually.

Positron is great.
Yeah.

♪ ♪

Through decades of experiments,

physicists have figured out
so many recipes

describing what the universe
is made of

at the tiniest of scales.

Groups of quarks make a proton.

Protons, neutrons and electrons
make atoms.

Atoms combine to make molecules.

Together, they make the stuff
we know and love.

Today, the biggest particle
accelerator is at CERN,

near Geneva, Switzerland,

where physicists recently
detected a new particle,

the Higgs-Boson, which gives
normal matter its mass,

and they're still looking
for more.

The question is: is dark matter
anything like ordinary matter?

Is dark matter some other
kind of particle

we just haven't detected,
haven't found yet?

♪ ♪

WILLIAMS:
The answer must lie
at the intersection

of particle physics
and astronomy.

♪ ♪

Peter Fisher was one of the
first to bring particle physics

to the dark matter problem.

♪ ♪

PETER FISHER:
Finding out what dark matter is

has been something
that's really driven

more by particle physics
than by astronomers.

WILLIAMS:
For decades, physicists
like Peter have focused on

a theoretical particle
called a "WIMP."

Weakly Interacting

Massive Particle-- or WIMP.

I think there was a lot of work

that went into finding
that acronym.

♪ ♪

WILLIAMS:
In order to create
the kind of gravity

that draws large amounts
of matter together,

the particle would need
to have mass,

but because it's invisible
and eludes detection,

it also must be
"weakly interacting."

FISHER:
So I think of dark matter
as kind of ghosts.

We don't see them because they
just don't interact very often.

What that means is that a WIMP

could pass right through
the earth,

without hitting any of the atoms
in the earth.

In fact, if you lined up
a hundred billion Earths,

a WIMP would go right through.

WILLIAMS:
So how do you capture
such an elusive particle?

♪ ♪

Peter Fisher spent 20 years
building machine after machine,

attempting to do just that.

♪ ♪

My students, postdocs and I

have built hundreds of these
different experiments.

Hundreds!

There's the remnants
of three sitting right here.

This is really kind of a mess.

Every experiment we build
is bigger and more complicated.

WILLIAMS:
And with each generation,

the experiments not only
got larger and more complex,

they went further underground.

♪ ♪

The hunt for WIMPs brought
particle physicist Ken Clark

here to this mine in Canada.

CLARK:
We try to detect them

in a much more physical way.

We're actually looking for
this dark matter to interact.

And that's what most of the
major dark matter experiments

right now are trying to do.

♪ ♪

WILLIAMS:
There are four different
experiments at Snolab.

At 6,800 feet underground,

it is one of the deepest labs
in the world.

It has to be.

CLARK:
All the time, all around us

there is cosmic rays
and there's particles

that are streaming in
through the earth's atmosphere,

and that kind of thing.

If we were to set up our
experiments here on the surface,

we would be completely swamped
by those signals.

WILLIAMS:
Instead, the experiments
are brought here,

a mile underground,

into special caverns
blasted out of the bedrock.

♪ ♪

The laboratory functions
as one giant clean room,

to keep the experiments
free from interference.

CLARK:
One fingerprint
on the experiment

would make it unusable.

It would be too dirty for us
to actually use.

♪ ♪

WILLIAMS:
The largest of the caverns
down here houses

the DEAP 3600 experiment.

It's the biggest liquid argon
dark matter detector

currently in operation.

So this is our cryo coolers
right now.

They keep the temperature
at -200 degrees Celsius

in the detector.

WILLIAMS:
Inside this huge vat
is the liquified gas argon.

It has to be kept
extremely cold--

almost at absolute zero.

Inside, the idea is that
the argon atoms are so cold

they are barely moving.

If any foreign particle
were to fly through the argon,

even if it were
weakly interacting,

it might hit
one of the argon atoms,

setting off a chain reaction
and trigger a detection.

♪ ♪

So far,
the huge ultra-cold experiments

have yet to yield
any dark matter.

The dark matter from outer space
so far has been missing.

None.
(chuckles)

WILLIAMS:
Just down the hall,
Ken Clark's experiment

takes a slightly different
approach.

He's not freezing things,
he's looking for them to boil.

The experiment starts
with a container

full of superheated liquid
made of carbon and fluorine.

It's placed under high pressure
to keep it from boiling.

Which means it's at
a temperature

above its normal boiling point
at this pressure,

so any little deposit of energy
means it boils instantly.

WILLIAMS:
Under these conditions,

if a particle enters
the liquid from outside,

it could immediately push the
liquid past the boiling point.

We're looking for the
dark matter particle to come in,

hit one of the fluorine nuclei,

cause it to recoil
that tiny bit,

and then cause a bubble in here.

WILLIAMS:
Custom-designed cameras
are constantly filming...

waiting for a bubble,

but they haven't found
a WIMP yet.

CLARK:
So far, this one has detected

exactly zero dark matter
particles.

But we're hopeful
that the next generation

we're going to actually
see something in it.

♪ ♪

WILLIAMS:
Back at M.I.T.,

it's a familiar story
for Peter Fisher.

FISHER:
In hundreds of experiments

we've never seen what we know
to be a WIMP.

♪ ♪

I've been doing this
for 35 years,

and so you might think that
not having detected a WIMP,

I would be frustrated by that.

Maybe a little bit,

but as a scientist,
what's exciting

is building something
and seeing it work.

Someday these ideas
might really shape

how we think of ourselves
as-as living beings.

♪ ♪

WILLIAMS:
We may not yet know
what dark matter consists of,

but we do know
what it's been doing.

♪ ♪

Ever since the Big Bang,

(explosion)

dark matter's gravity has been
drawing the universe together.

Once astronomers realized this,

they began to wonder what
this might mean for the future.

KAISER:
We know the universe
is filled with ordinary matter.

It's chock full of dark matter.

The gravitational tug
of all that matter

should have sort of slowed
the rate at which the universe

as a whole continued to expand.

Maybe the expansion itself
could literally halt,

maybe even leading to a reverse
Big Bang--

the Big Crunch.

Think about the simple act
of throwing a ball.

Every time I throw the ball up,

gravity will slow it down,
and at some point,

will pull it...
back to earth.

So could this happen to all
the stuff in the universe?

We know that everything
in the universe

is flying outward right now,
but how long will that last?

Could it be like this ball?

Slowing down,
eventually reversing direction,

and returning
to where it came from.

What would that mean for
the future of the universe?

♪ ♪

WILLIAMS:
In the late 1990s,
two groups of astronomers--

including Saul Perlmutter

and Alex Filippenko...

8.83 arc seconds north.

WILLIAMS:
...were trying to answer
that very question:

as the universe was expanding,
would gravity slow it down,

and eventually pull it back
together?

FILIPPENKO:
The original goal of our project

was to measure the rate at which
the expansion of the universe

is slowing down.

♪ ♪

WILLIAMS:
They set out to measure
the speed of the universe

as it expands outward and detect
how much it's slowing down.

But how do you do that?

Turns out,
there's a kind of star

that's perfect for this
measurement-- a supernova.

Yeah, right there.

Oh yeah,
it might be right there.

FILIPPENKO:
A supernova is simply
an exploding star.

Now most stars, like our sun,

will die a relatively
quiet death,

but a small minority
literally destroy themselves

in a titanic explosion
at the end of their lives,

becoming millions
or even several billion times

as powerful as our sun.

PERLMUTTER:
Because they're so bright,
this one object can be seen

ten billion light years away
and further,

so already that's interesting.

WILLIAMS:
The team needed
a particular kind

of supernova called a Type 1a.

(explosions)

Their explosions always reach
a certain peak brightness,

allowing astronomers
to calculate their distance

from Earth.

Like headlights on a road,
the dimmer they appear,

the farther away they must be.

But first, astronomers
had to find them.

Is it there
or is it not?

FILIPPENKO:
Supernovas are pretty rare.

Roughly once per galaxy
per century,

or even per several centuries.

(indistinct chatter)

WILLIAMS:
Astronomers had to survey
thousands of galaxies at once

looking for this
needle in a cosmic haystack.

In five minutes,
we'll know.

WILLIAMS:
Months of grueling observation

eventually yielded
a handful of 1a supernovae.

Hey, it's there!
We got something!

WILLIAMS:
From various times
in the history of the universe.

Okay,
let's keep on exposing.

WILLIAMS:
Not only could they determine
their distance,

but the teams could also gauge
how fast they were traveling

as the universe expanded.

They did this by measuring
something called "redshift."

Redshift is caused
when light travels

across regions of space
that are expanding.

As the fabric of space
stretches,

so too does the wavelength
of light,

shifting toward the red
end of the spectrum.

By analyzing the redshift
of different supernovae,

the teams could see how fast
the universe was expanding

and stretching at different
times in its history.

PERLMUTTER:
We ended up with a pool

of some 42 supernova
mapping out the history

for some seven, eight
billion years,

to see when was it
expanding faster,

when was it expanding slower,
and we looked to see whether

it was slowing down enough
to come to a halt.

Okay, here we go.

♪ ♪

WILLIAMS:
But when they finished
processing their data...

MAN:
I'd be a little suspicious
of that one, guys.

WILLIAMS:
...something did not look right.

PERLMUTTER:
When we actually finally
made the measurement,

we came up with this
bizarre result.

♪ ♪

WILLIAMS:
The supernovae were much
farther away than they expected.

Meaning the stars
and their galaxies

were traveling much faster
than anyone predicted.

KAISER:
As they pieced these pieces
of the puzzle together,

the teams found,
much to their own surprise,

to the real tremendous surprise
to the community at large,

was that the universe
is not slowing down

in its expansion at all.

Instead, these surveys showed
the universe is speeding up

in its rate of expansion.

It's not just still expanding,

it's expanding faster and faster
over time.

WILLIAMS:
The universe was not just
expanding-- it was accelerating.

And that's like, oh my gosh,
in a multiple choice test,

that's not one of the options.

And my jaw just dropped.

FREESE:
This is revolutionary.

The universe is accelerating?

(laughing):
If I had a ball
and it just started moving

in that direction,

moving faster and faster
and faster,

but no one was throwing it,
or there was no force,

that would be weird, right?

That would be weird.

WILLIAMS:
Some unknown force
was pushing the universe apart,

challenging everything
we thought we knew

about the cosmos.

Scientists dubbed it
dark energy,

and they soon determined
there was a lot of it.

It's 70% of the contents
of the universe!

70%!

Seven zero.

It's far and away
the largest contributing factor

to all the stuff
we can otherwise add up

in the universe today.

♪ ♪

WILLIAMS:
So what exactly
is this weird stuff

that makes up the vast majority
of our universe?

In a sense,
dark energy is a term that

illustrates our ignorance
of what's actually out there.

We don't know what it is.

♪ ♪

FRANKLIN:
This is a case where
it's kind of a mystery,

and even hard to think about,
even for normal physicists.

♪ ♪

WILLIAMS:
One idea is that the energy

comes from some
undiscovered particle.

Another says our understanding
of gravity is not quite right.

And then there's
the most popular theory.

FILIPPENKO:
Perhaps the simplest,

and one which is not yet
ruled out,

is that the dark energy
is simply the energy

associated with
the vacuum of space.

It's just part of space itself,
it's not something in space,

it's just part of what space is.

WILLIAMS:
But it's a part of space
that creates more space

over and over again.

It almost sort of
feeds on itself.

So, dark energy is what's
stretching the universe

at a faster and faster rate and
it's literally making more space

and dark energy
is an energy of empty space.

So, it's made more empty space,

which has in its own,
more dark energy.

It's the only form of energy
that we know that is capable

of doing that.

To make spacetime expand
faster and faster.

(laughing):
It's very weird.

It's crazyland!
It's very weird!

We have no idea what is
the physics underlying it.

WILLIAMS:
Marcelle Soares-Santos
is trying to figure out

the physics behind dark energy.

Because it's really about
figuring out

something that we have no idea
what it is.

WILLIAMS:
She's part of the
Dark Energy Survey--

an international research
initiative.

We want to know, really,

what is the precise nature
of dark energy.

Okay, so redshift is .2...

WILLIAMS:
Josh Frieman leads
one of the teams

based at Fermilab
outside Chicago.

The strategy is to try to track
how fast the universe

is accelerating
as precisely as possible.

It turns out that
the more precisely

we can measure how fast
the universe is expanding today,

the better job we'll do
in trying to figure out

what dark energy really is.

WILLIAMS:
Back in the 1990s,
the discovery of dark energy

was based on
just a few dozen supernovae.

♪ ♪

But today, the Dark Energy
Survey can do much more.

Powerful telescopes--

like this one on a mountaintop
in Chile--

scan huge swaths of the sky.

With so many images and powerful
computers to analyze them,

the team has collected
thousands of new supernovae,

each one a snapshot
of a different point

in the universe's history.

♪ ♪

But there's another set of clues
that might help paint

a clearer picture
of this mysterious dark energy.

(phone vibrating)

And that's why Marcelle
was so excited

when signs of a gigantic
cosmic explosion

recently reached Earth.

This was something that we were
all preparing for a long time.

WILLIAMS:
130 million light years away,
two neutron stars had collided.

(explosion)

The explosion was so powerful,
it sent gravitational waves,

ripples in the fabric of
spacetime, across the universe.

SAURES-SANTOS:
We received a signal
from LIGO and Virgo.

(bell ringing)

WILLIAMS:
Like the ringing of a bell,

the waves trigger sensors
here on Earth

at LIGO in the U.S.,

and Virgo in Italy.

Astronomers around the world
point their telescopes

towards the source
of the signal,

trying to find the light
from the explosion.

SAURES-SANTOS:
We're looking for the light
corresponding to that "sound"

that the gravitational wave
detectors just heard.

WILLIAMS:
And then they find it.

From Earth, a tiny dot
that wasn't there before.

Several research teams
around the globe spot this dot.

Oh... this was fantastic.

WILLIAMS:
Fantastic because,
for the first time,

astronomers both "hear" and see
a distant cosmic event.

(popping)

That is the first ever...

for any astronomer.

♪ ♪

WILLIAMS:
That alone is remarkable.

But for the Dark Energy Survey,

this type of event has opened
a new window on the universe.

SAURES-SANTOS:
With the gravitational
wave data, we can do more.

The gravitational wave's signal
contains information

about the distance to the source

that is independent
from the light.

WILLIAMS:
Gravitational waves provide a
whole new source of information,

helping to pinpoint the distance
to these violent collisions.

And having two independent
sources,

both seeing and hearing
an event,

could reveal how fast the
universe was stretching apart

at the moment of the explosion.

(explosion)

SAURES-SANTOS:
Now we have a new way
to attack the problem.

We can determine how fast
the universe is expanding

in between, and voila, we have
information about dark energy.

WILLIAMS:
For the team,
combining gravitational signals

with more tiny dots
like this one

might someday help reveal
what dark energy actually is.

(camera clicking)

SAURES-SANTOS:
Everybody knew that we were,
in some sense,

witnessing the birth of a new
field, a new area of research.

WILLIAMS:
Astronomers may not have cracked
the dark energy mystery,

but the last 20 years have
uncovered a new dramatic story:

the ongoing epic struggle
across the cosmos

between dark energy
and dark matter.

Astronomers are convinced
that these are

the two major players
in the universe:

dark matter, pulling
the universe together,

and dark energy,
pushing the universe apart.

(rumbling)

They're engaged
in a cosmic tug of war

that will determine nothing less
than the fate of our universe.

They're really literally pulling
in opposite directions.

So we know that dark matter
and dark energy

are in the grips of this
cosmic competition,

and which side, so to speak,
has been winning

has itself changed over time.

WILLIAMS:
With each discovery,
we're getting a clearer picture

of how this battle
has played out

since the birth of the universe.

Just after the Big Bang,

the universe was literally
a hot mess,

sizzling with radiation until
dark matter and matter formed.

Dark matter and its gravity

became the dominant driver
in the universe,

pulling together gas and dust,

allowing galaxies and stars
to form.

FISHER:
And there was a time

where normal and dark matter
dominated the universe.

♪ ♪

WILLIAMS:
In fact,
for nearly nine billion years,

dark matter's gravity
was so strong

it was slowing down
the expansion of the universe.

But then, something changed.

About five billion years ago,

the universe started
accelerating in its expansion.

This moment-- when the universe
stopped slowing down

and suddenly started
speeding up--

is known as the cosmic jerk.

FISHER:
And really, starting
just a few billion years ago,

dark energy came to dominate
the universe.

So, I would say we have evolved
into a dark universe.

♪ ♪

WILLIAMS:
Around the world,
researchers continue the hunt,

determined to find
the secret ingredients

that make the universe--
and everything in it-- possible.

FRANKLIN:
You have people looking
on all sides.

And somehow all of those things
together are going to help us

to understand.

It's kind of an incredibly great
example

of how science
should really work.

That everybody should just
follow their own curiosity

and intuition.

And then together,
it'll be brilliant.

♪ ♪

SAURES-SANTOS:
It is a little bit humbling

to look out there
in the universe and say,

"Most of it I don't understand."

But at the same time,
of the part we do understand,

we understand it so well
that we were able to transform

the world around us
based on our knowledge.

And all of that success
makes us confident

that we will succeed here
as well.

LYKKEN:
We're just scratching
the surface.

The whole history of science

is finding out that the universe
is bigger and more complicated,

and more mysterious
than anybody had thought.

We found out the earth
was a planet,

and then we had a solar system,

and we have a galaxy,

and we have billions
and billions of galaxies.

And where's the end of that?

We don't know.

That is a big mystery.

♪ ♪

"NOVA Wonders"
is available on DVD.

To order,
visit shop.PBS.org,

or call 1-800-PLAY-PBS.

"NOVA Wonders" is also available
for download on iTunes.

♪ ♪