Original subtitles

Until recently, scientists thought

that everything in the universe

from the things surrounding us on earth

to the stars in the sky were all made of matter

that was composed of atoms and molecules.

However, the data accumulating from a number of sources

have made it clear that an unidentified mystery matter

also exists.

Its quantity is hardly negligible.

This dark matter as its called may amount to five times

as much as ordinary matter.

Yet we can neither see it nor feel it.

Now, scientists all over the world are competing fiercely

to be the first to discover actual dark matter.

In Europe, the effort to reveal the identity of dark matter

centers on reproducing the super high energy fields

of the creation of the universe.

In the United States, an experiment has began

based on the premise that dark matter

transforms into weak electrical impulses.

How did scientists realize that such an illusive substance

even exists?

And how can they know it pervades our universe

when its very form is unknown?

This is the story of dark matter and of the scientists

who are searching so passionately for it.

We cannot see air yet we know its composition.

However, while we know that dark matter surrounds us

even more pervasively,

no scientist has been able to determine its composition.

Some 85% of all the matter

in the universe is mystery matter.

This facility in Central Japan was built with the hope

of providing the world's first real glimpse of dark matter.

In the spring of 2010, NHK cameras were allowed in

for the first time

to film the XMASS detector as it was being fitted

with super sensitive light sensors

called photomultiplier tubes.

But why are scientists go in a thousand meters underground

to use this device?

It's because the thick bedrock shields the equipment

from being influenced by any matter other than dark matter.

Yoichiro Suzuki of the University of Tokyo

calls this facility an underground observatory

that will solve one of the universe's greatest mysteries.

For a number of years, many scientists have,

like Suzuki, postulated that dark matter is a new type

of particle called a Supersymmetric particle.

But evaluating the numerous candidates

has proved to be a long and winding road.

First, the story of how scientists realized

that dark matter even exists.

This is the Carnegie Institution for Science

in Washington, DC.

Here a party was held to celebrate 45 years of service

to the institution by a pioneering female scientist.

You now have a Carnegie service hand, Vera Rubin

Thank you.

May I say a word?

Vera Rubin, age 82.

I have two words two say.

One of them involves Dave for many more people, yeah.

It was Rubin who released to the world

the data that served as the starting point

for the search for dark matter.

Fascinated by the stars since childhood,

in high school she began to cast her thoughts seriously

towards the cosmos using a homemade telescope.

In college she confidently set her sights

on becoming a professional astronomer.

These are special pictures because most of them

have been... Her research topic involved gauging

the velocity of stars within various galaxies.

The Andromeda Galaxy, for example,

hundreds of billions of stars swirl around its center.

Rubin devised a way to derive velocities

for the stars marked with black dots in this image.

Galaxies outside our own are so distant

we can't actually see their individual stars moving.

But if the wavelengths of the light

from those stars are analyzed,

the stars' velocities can be determined indirectly.

Let me show you what it looks like,

what you get from a telescope.

This is a spectrum of an object.

And from this we can get an exact

measure of how much the object is moving.

I guess most people know that if you have a

whistle or airplane or something is flying,

something is moving fast past you,

it will seem to shift to change its

radiation at the optical sense.

So stars do the same thing.

Rubin's observations made use

of the well known phenomenon of the Doppler effect.

For example, as a train approaches,

its sound travels smaller distances,

a shrinking sound wavelength

heard as a rising pitch.

As it pulls away, the opposite occurs,

longer sound waves and a falling pitch.

A similar phenomenon occurs with light.

The light of an approaching object

has a shrinking wavelength.

So it appears bluer than its true color.

As the same object recedes, wavelengths increase

and the object looks redder.

Using a similar logic,

Rubin determined the velocities of stars

by measuring changes in light wavelength.

The data, however, led her to a startling conclusion.

The stars were moving at much

faster velocities than predicted.

So what was keeping these stars and other objects

in their galaxies instead of being flung out of them?

The data could only be explained

by the existence of something invisible

with enough gravitational force to keep the stars

anchored to their galaxies.

There had to be much, much, much, much

more matter further out than anyone

had ever expected.

And if you do the arithmetic, it's pretty simple.

This discovery is what brought dark matter

to the world's attention for the first time in 1970.

However, the suggestion that the galaxies contain

large quantities of an invisible substance

drew fierce criticism from the scientific community.

No one believed it.

The people we spoke to

would tell us that you can't do it,

the data aren't good enough.

Person next to me was a rather great astronomer.

He spent the whole evening telling me why

I couldn't do what I did.

And I don't know how good those data were.

Despite this cold professional reception,

Rubin persevered undaunted.

In applying to graduate schools,

she had encountered rejections simply because

she was a woman.

She says this experience helped her later

in dealing with colleagues' prejudices.

By the end of the 1970's,

she uncharted the movements of stars

in more than 100 galaxies.

Her results proved that in all these galaxies,

stars were moving at faster velocities

than had been predicted.

These observational data definitively established

the existence of an invisible substance

acting on the stars.

So this was the first time in astronomy, I think,

that people had really inferred the existence of something

from gravity alone without actual evidence

from light, from photons.

So it wasn't a rare thing.

It wasn't just here and there, it was in every galaxy.

And we needed to understand that,

what it was, where it came from

in order to make our whole picture of galaxies.

What was the source

of this gravitational force holding a galaxy together?

Starting in the 1980's, the challenge of dark matter

was taken up by a legion of scientists.

The first hypothesis that attracted many scientists

was that dark matter was actually made of numerous

dark stars invisible to observation with telescopes.

David Bennett of the University of Notre Dame

is one of those who used to believe that dark matter

is composed of dark stars that do not emit light.

When most people try to imagine a star

that does not emit light,

they are likely tot think of a celestial body

so small in mass compared to a radiating star

that it's more like one of the planets of our solar system.

By the mid 1980's, however,

scientists knew that the universe does include

many dwarf stars and black holes

and other extremely massive objects that do not emit light

but may exert powerful gravitational forces.

We thought the dark matter...

Establishing that dark matter

is actually comprised of dark stars would require

proving the existence of massive dark stars

in numbers far greater than radiating stars.

The conceptual tool Bennett decided to apply

was gravitational lensing.

It was Albert Einstein who first proposed

gravitational lensing in 1936.

Instead of traveling straight, he theorized,

light from the star would be bent by a massive object

exerting a powerful gravitational force.

So if a dark star cut across the path of a radiating star,

the light from the radiating star would temporarily

appear to increase as the dark star passed

before returning to its original brightness.

We can consider, this little flashlight

to be a a background star and then

this glass will represent the foreground object

it surpasses in front, it distorts the image and

the effect of that distortion is that we see the object

appeared to get brighter and then dimmer again.

The plan was simple, find stars that get brighter

and then return to their original brightness.

If dark matter was indeed massive dark stars,

a little perseverance should suffice to prove that.

A colleague of Bennett's thought this plan too simple.

Later on when he wrote something about it,

he attributed my enthusiasm due to the fact

that I didn't have any observing experience

and didn't know how hard it would be.

And I thought that was just great because here,

you know, as a case where you could do a measurement

and you either found the dark matter or you ruled it out.

Bennett's idea instantly attracted worldwide

scientific attention.

He rapidly assembled a team of 25 scientists

from six nations to join the search for massive dark stars.

The team trained a super sensitive telescopic camera

on a region that they have divided

into 82 sectors for analysis.

They then made daily observations of any changes

in the brightness of more than 10 million stars.

After three years of observations,

Bennett's group discovered a phenomenon

that brought them even more recognition.

The science journal Nature carried photos

of a star that flashed violently bright then subsided.

Researchers around the world were thrilled

by this definitive proof of the existence

of massive dark stars.

Over time, however, the idea that dark matter phenomenon

were explained by dark stars gradually lost support.

In seven years of research, Bennett and his colleagues

discovered no more than 13 dark stars.

A whole course of critics insisted that for dark stars

to account for dark matter, more than a hundred set stars

should have been discovered.

Bennett and his team had ended up proving

ironically that dark stars alone could not be the source

of those powerful gravitational forces.

But it could be that some galaxies also

form a lot more of these brown dwarfs than others do.

That's a possibility.

It might be a little bit difficult to tell.

But I think, you know, that the vast majority

the dark matter has to be in some other form.

Back when Bennett was hunting for dark stars,

another researcher was taking a holy different approach

to identifying the composition of dark matter,

Mitsuhiro Nakamura of Nagoya University,

his field is particle physics

which had developed rapidly in the latter half

of the 20th century.

He started from the premise that dark matter

is an elementary particle.

Since ancient times,

scientists have been searching for new elements.

In the 1970's there had been a recognized list of particles

making up all matter.

There were the electron and six types of quark

and other particles.

They were held together by exchange particles

such us the photon and the gluon.

It as thought that all the matter in the universe

could be described as various combinations

of the 25 particles on this list.

For example, protons are comprised of two up quarks

and one down quark held together by gluons.

Protons and electrons bound by photons

make up hydrogen.

The individual who compiled that master list of particles,

a co-winner of the Nobel Prize in 2008,

was Toshihide Maskawa.

The general theory of particle physics worked on by Maskawa

and others is referred to as the Standard Model.

The general opinion at the time was that

all physical phenomena in the universe

must be explainable by the Standard Model.

Nakamura,

on his quest to identify the mysterious dark matter,

was convinced that it would be found

somewhere on the list indicated by the standard model.

Narrowing the list down to possible candidates

for dark matter did not take very long.

The first to go were the components of normal matter

such as hydrogen namely the up quark,

the down quark, and the electron.

Then the particles that bind the others together:

the gluon and the photon.

Finally, Nakamura illuminated the most short lived

unstable particles.

What were left were only three types of neutrino.

It was known that the universe contains

an immense number of neutrinos.

And that neutrinos had the ability

to pass through other matter

so they were highly suitable candidates for dark matter.

If an individual neutrino has more than

a certain mass, the dark matter problem is solved.

So Nakamura and his colleagues,

using devices they built themselves,

started measuring the mass of various neutrinos.

At that time in Japan,

another neutrino experiment was also taking place.

A research team at the University of Tokyo

was using a gigantic device called the Super Kamiokande.

Fitted with over 10,000 optical sensors,

the Super Kamiokande succesfully measured

the precise mass of neutrinos.

The result showed that even the heaviest

of the three candidate neutrinos did not posses

1/100th of the mass postulated by Nakamura.

Neutrinos were now disqualified as potential dark matter.

So now both dark stars and neutrinos

were out of the running for dark matter.

There was no shortage of alternative theories.

But by the end of the 20th century,

the search for dark matter was foundering.

Vera Rubin had been ahead of her time

in championing the existence of dark matter.

When scientists lost the trail of dark matter

she was in her 70's and still a stargazer.

I could see them from my window.

I didn't have to leave my bed

and really after a while it was more interesting to

watch the stars than to go to sleep.

Continuing her professional observations

of the heavens, Rubin tried to turn scientists' attention

once more to dark matter.

She insisted that fresh data were needed.

I didn't know

if we were missing something,

if there was something I had not done

that should be done.

I mean, it was certainly initially,

it was so strange and so unexpected that

I felt that I better keep going.

In the 21st century, just as Rubin had wished,

new data came flooding in.

Three, two, one, main engine start.

In 2001, NASA launched WMAP.

It was designed to provide a precise map

of the universe's microwave background radiation.

From the varying intensity of that radiation,

it could determine temperature distributions

throughout the universe.

From those patterns, you could further calculate

the total mass of all the matter in existence.

The results were astonishing.

If one adds together, the mass of all the ordinary matter

in all the galaxies and interstellar gases

observed so far, it amount to no more than

15% of the total matter in the universe.

Here was confirmation that 85%

was comprised of an unknown substance.

It transpired that dark matter

not only helped formed our stars and galaxies

but ultimately was essential to the origin of life.

Naoki Yoshida of the University of Tokyo

has created a computer simulation of the universe

in the moments just after its creation.

He found that without dark matter,

even if one assumes that the universe is born,

nothing comes of it.

The Big Bang is said to have happened

13.7 billion years ago.

At that moment, many kinds of matter were created.

If there were no dark matter

and the universe consisted purely of ordinary matter,

how would things have developed?

Given a billion years or even 10 billion years,

matter cannot coalesce by the force of its own

gravitational attraction and not a single star

shines in the heavens.

If stars cannot form then there will be no oxygen or carbon,

those elements of life.

In this simulation, however, along with the ordinary matter,

dark matter exists.

As soon as the universe is born,

the gravitational power of dark matter

helps ordinary matter take shape.

Eventually, a sufficient mass is built up

so that 300 million years later,

the first star in the universe is born.

Dark matter even supports the formation of the galaxies

which start taking shape a billion years after the Big Bang.

Later, the countless galaxies that have formed

are distributed in large scale structures

that resembled bubbles or nets.

These structures would also had been impossible

without the gravitational force of dark matter.

All in all, without dark matter,

the universe as we know it could never have formed.

In one of his simulations, however,

Yohida found something that might help to get a fix

on dark matter.

He determined that if dark matter plays a key role

in forming stars and galaxies,

a mass tens to thousands of times that of a hydrogen atom

would be consistent with the type of heavy particle

dark matter would have to be.

This was the conclusion indicated by the combination

of Yoshida's simulations with other scientific data.

So what could this candidate particle be

with a mass tens to thousands of times

that of hydrogen?

It had never been found anywhere.

A clue to the composition of dark matter

appeared from a completely unexpected source.

Pierre Ramond is a theoretical physicist.

His forte lies not in observation or experimentation

but in using pure mathematics

to uncover the laws of physics.

Presumably, if you were to write closed form formula

like this, you would put this to some power.

It's fascinating that there are always simple answers

to complicated questions.

And that is something that, you know,

which never ceases to amaze me.

The world of elementary particles...

One of Ramond's proposed improvements

was an important attribute that he said was missing

from the Standard Model, namely Supersymmetry.

Supersymmetry turned out to be related to dark matter

in an unexpected way.

What exactly is Supersymmetry?

This highly mathematical concept is difficult to explain

to non-experts so Ramond likes to use

the following illustration.

So you see me waving my right hand.

And here in the mirror, if you look in the mirror,

you will see that it looks like I'm waving my left hand.

So imagine that I'm a particle

and I'm like this and then whatever this person is

looking on the other side of this,

they're Supersymmetric particles from this.

But now, okay, Francisco, please, if you could...

Ramond deploys another mirror.

Okay, so.

This way.

Yes, that is fine.

Come closer.

Yeah, that is perfect.

So now, if you look at this mirror,

you will see that I am back to waving my right hand.

So this is me, this is my antiparticle

and yet this is back to me except I have moved a little bit.

And in some sense, the analogy would be

that you make two Supersymmetry transformations

and it is like you have moved a little bit.

There is one reason in particular

while Ramond now thinks Supersymmetry

important to dark matter.

It could provide the solution to a mathematical deficiency

in the Standard Model that had been pointed out

for many years.

In the Standard Model, one of the calculations

yielded a value of infinity, a meaningless result.

When the theory it augmented with Super Symmetry, however,

the infinity disappears.

So therefore, that conceptual problem

in a Standard Model can be actually solved by

adding Supersymmetry to the model, okay?

Using the hint provided by Supersymmetry,

Ramond is now attempting to derive ultimate laws of physics

that will go beyond the Standard Model.

But his argument has hit a snag.

He now has to establish the existence of mirrored versions

of the particles listed in the Standard Model,

a corresponding list of Supersymmetric particles.

With not a shred of evidence that such particles exist,

he has reached the limits of what theory can do.

Ramond's mathematical refinements, however,

have suggested to some researchers

that dark matter may in fact be a Supersymmetric particle.

The idea here is that you get a tight constraint from

what could have been detroyed.

One of them is Hitoshi Murayama

of the University of Tokyo.

He points out that if the dark matter sought by astronomers

and the Supersymmetric particles conceived of

by theoretical physicists are actually the same

then a whole variety of outstanding problems

will be solved simultaneously.

The latest Supersymmetric models

yield a high probability that Supersymmetric particles

would include one that is several tens or even thousands

of times heavier than hydrogen.

As the computer simulation of the universe's evolution

showed, such a particle would be a perfect candidate

for dark matter.

Pervading both us and the material world we live in

is a huge amount of invisible dark matter

in far greater quantities than the visible matter

we are used to seeing.

An aspect of reality so strange,

one can scarcely believe it exists

and yet its existence is beyond doubt.

Currently, research teams around the world are competing

in the search for dark matter.

One specific goal,

the discovery of Supersymmetric particles.

The best funded of these efforts is conducted

by the European Organization for Nuclear Research, CERN.

CERN is using its Large Hadron Collider,

the world's largest particle accelerator,

to smash protons experimentally.

In this huge device, nine kilometers in diameter,

they recreate the high energy conditions

that obtained just after the Big Bang

when Supersymmetric particles may have been created.

The goal is to produce

Supersymmetric particles artificially.

John Ellis has been conducting research at CERN

for nearly two decades.

He strongly supports Supersymmetric particles

as candidates for dark matter.

And he's positive that they will discovered at CERN.

But even if hypothetically,

you could create a Supersymmetric particle,

how could you confirm the existence of something

that is invisible?

Ellis contends that if you meticulously track energy flows

just before and after proton collisions,

you will be able to prove the existence

of these invisible entities.

So often they make collisions where

a lot of particles come out on one side

that of energy.

And then usually that energy is found on the other side.

And so the energy one is approximately the same

as energy two.

Okay, this is what normally happens.

Now, when you have dark matter,

you would have in addition particles

that you don't see.

So it would carry away invisible energy.

And in that case, the two energies would not balance.

In a collision,

roughly the same amount of energy is discharged

above and below the collision path

so the total energy balances out.

But when invisible dark matter is created,

the balance is compromised

and the energy does not equalize.

That would be considered proof of the presence

of dark matter.

At CERN, they have already observed some

three trillion collisions

compiling a massive amount of data.

But at present, they still have found no proof

of the existence of dark matter.

The search for dark matter is heating up all over the world.

Nowhere our expectations greater

than for the research team in Japan.

XMASS began operating in April 2011.

There are two reasons why it has attracted such high

expectations from around the world.

One is that this is a unique device

for detecting the Supersymmetric particles

that are thought to comprise dark matter.

It is filled with liquid xenon that has been cooled

to minus 100 degrees Celsius.

Xenon was chosen because of a particular feature,

its atoms weigh about 130 times those of hydrogen.

In other words, about the same as the predicted weight

of the Supersymmetric particles.

Suzuki's hypothesis can be illustrated

with a following analogy.

Dark matter is all pervasive.

Even when it enters the xenon,

most of the time, nothing will happen.

But on very rare occasions,

some dark matter will hit a xenon atom and move it.

Since their mass is about the same,

the energy of the first atom will be transferred

to the second as in a collision of billion balls.

That observable energy transfer will prove the existence

of dark matter.

Scientists also have high expectations

for the array of super sensitive optical sensors

surrounding the liquid xenon inside XMASS.

These sensors called photmultiplier tubes

were specially developed to detect the minuscule

amounts of light released by the xenon atoms

impacted by dark matter.

The research team is monitoring their

642 sensors around the clock.

It is estimated that some 2,00 units of dark matter

entered the device every second.

And the probability that one will impact a xenon atom

ranges from about once every few days

to once every 10 days or so.

Researchers thus estimate that within a year at the earliest

they will be able to identify dark matter.

40 years ago, Vera Rubin pointed to the presence

of something in the galaxies that exist

but cannot be seen.

Here are some of the books and the little globes.

Yeah, the ones I like the best are these.

They're pretty old.

I've forgotten.

You can take it our for sure.

Yeah.

Yeah.

No one is more surprised than she

that the contemporary debate over dark matter

which began with her observations of the cosmos

now extends to Supersymmetry

and the search for the ultimate laws of physics.

This is our sun and this is...

Rubin cautions that in the face

of such mysteries, scientists should always precede

with humility.

I'm a little skeptical about some of the

models of the universe

because you're going out so far.

But in the sense, I mean, that's how science goes.

If you do the best you can,

you make the best suggestions or guesses

or whatever you wanna call them.

And there's probably some right in them

and there's probably some wrong in them because

we're not very good at imagining very different things.

The search for dark matter began

with the persistence of the single researcher.

In their effort to resolve the riddle of dark matter

bound up as it is with the search

for Supersymmetric particles,

what new horizons will scientists behold?

Will their pursuit give rise to further mysteries?

And so continues the epic quest for dark matter.