How the Universe Works

Across the universe, an endless war rages,

a bitter struggle between invisible forces.

We've seen this cosmic battle go on

for the past 14 billion years.

Like two navies, fighting it out in the ocean of space time.

Dark matter...

And dark energy

battling for control of the universe.

They've shaped the entire history of the universe.

They're not about to stop now.

Shadowy forces dictating our past,

our present, and our future.

The dark universe is kind of a puppet master

behind the scenes,

guiding the universe that we can see.

It's taken over the universe and, eventually,

it may well destroy the universe.

Captions paid for by Discovery Communications

As we look out across the universe,

we see nebulas,

stars,

and planets,

all constructed from visible matter.

But what we see is just a small part of the cosmos.

The rest is invisible, unknown...

The dark universe.

Dark universe is a very common phrase to describe our universe,

because it turns out most of our cosmos is dark.

Dark not as in night.

Dark as in, doesn't interact with light,

and dark as in, we don't really understand it.

All the objects in our daily experience...

Our bodies, the air, the chair that you're sitting in,

the planets and stars,

all of that only adds up to 5 percent of the universe.

It's the other 95 percent that is the dark stuff,

the dark universe.

The dark universe is made of two forces...

Dark matter and dark energy.

In a way, the dark matter and dark energy

sort of oppose each other.

Dark matter has positive gravity that pulls things together,

and dark energy has repulsive gravity

that pushes things apart.

To encapsulate that in one sentence,

dark matter is attractive, dark energy is repulsive.

Since the dawn of time,

two forces slugging it out for control of the universe.

Dark matter and dark energy

are locked in this epic struggle.

The dark matter is trying to bring things together.

The dark energy is trying to drive everything apart.

So it's basically a battle. Who's going to win?

It's a struggle that started 13.8 billion years ago

in the cosmic furnace of the big bang.

The infant universe was a super hot ball of intense radiation,

but suddenly...

...It started to transform.

It cooled and expanded,

triggering the birth of the regular universe

and the dark universe.

Scientists believe that both dark matter and dark energy

formed in the first moments of the big bang.

It would have formed probably just fractions of a second

after the big bang,

around the time that normal matter formed,

and the processes that created

the normal matter we know all about.

Similar processes probably created the dark matter.

During these first microseconds,

the universe was a hot, dense ball of matter and energy.

They're two sides of the same coin.

Matter can convert into energy...

...And energy can convert directly into matter,

visible particles of regular matter forming atoms,

planets, stars, and us...

And other particles.

They are invisible.

They are dark matter.

One of the big mysteries that we as astronomers have to solve

is what this dark matter is.

We just don't know.

The idea of a type of matter that you can't see

and that acts differently than normal matter

is sort of out there.

It's sort of weird.

But the dark universe does leave clues.

It's like a crime scene.

You know that a crime has been committed,

even though you don't know the perpetrator yet.

We see the hints. We see the signs.

We see the signals that something funny

is happening in our universe,

even though we don't know exactly what's causing it.

There are several contenders

for what dark matter could be.

It could be normal matter that we just don't see,

or it could be some sort of exotic matter,

a particle of some sort that we haven't detected yet.

It could be a species of particle,

like an electron, like a proton, like a quark,

but a special kind that doesn't interact with light.

One of the favorite possible models of dark matter

are wimps, weakly interacting massive particles.

Wimps may not interact strongly with other matter or light,

but they do exert a gravitational pull.

So they're the best candidates for the particles of dark matter

that formed in the big bang.

The early universe was intensely hot and dense,

full of new particles of both visible matter

and invisible dark matter.

But another force was present...

Dark energy.

Dark energy has existed since the time of the big bang.

Dark energy was always there.

We don't know how much of it there was,

but it's possible that the same amount of dark energy

was always there.

Our understanding of what that dark energy is

is very limited.

If you were to ask a roomful of 10 theoretical physicists

on the nature of dark energy,

you'd get about 12 different answers.

We're not sure what dark energy is.

Dark energy is just a fancy name for our ignorance.

Dark energy is nothing more than a placeholder name

for this enormous gap in our understanding

of how the cosmos works.

But we don't understand it at all.

It's true.

One potential answer to what dark energy

actually is may be found in so-called empty space.

Could this be the source of dark energy?

We used to think of space as just boring emptiness.

But now, I think it's healthier to think of space

as a kind of substance.

A substance that carries a strange type of energy.

Every small region of space

has a little bit of energy in it,

just associated with the vacuum itself.

Vacuum energy is the idea that vacuum isn't empty,

that there is something there.

There's an energy in it with a kind of antigravity.

Perhaps this vacuum energy

that pushes against gravity

is the mysterious dark energy.

We simply don't know.

We're not sure that the dark energy is the vacuum energy.

It could be a new type of energy that permeates all of space.

This is what we're trying to measure now.

Dark energy and dark matter,

forged in the intense heat of the big bang,

opposing forces, one attractive, one repulsive.

But together, over 13.8 billions years,

they will shape the history of the universe.

The story of the universe is dominated

by two powerful opposing forces...

Dark matter and dark energy.

For 13.8 billions years,

they've battled it out for control of the cosmos.

Dark matter and dark energy are out there,

and they've shaped the entire history of the universe.

Our universe is actually the balance between dark forces.

Dark matter is trying to draw everything together,

and dark energy is trying to rip everything apart.

After the big bang, the infant universe was small,

intensely hot and intensely dense.

Dark matter, the force bent on bringing things together, thrived.

But in this compressed space, dark energy,

the force trying to drive things apart, had no room to act.

When things were closer together,

the density of matter and radiation was bigger,

so big that the dark energy didn't matter.

The environment was also tough for normal matter.

It was so hot, intense radiation

prevented visible matter from bunching together to form atoms.

If any normal matter tried to clump together

through gravity or some other force,

this energy would just basically blast it apart.

In the very early universe,

when our universe was a lot smaller

and a lot hotter and a lot denser,

matter, normal matter, tried to collect together,

wanted to join the party.

But it was prevented from doing so

because there was also radiation that would throw it out.

Unable to stick together,

normal visible matter sped out

across the infant cosmos in a blizzard of particles.

But then dark matter,

the force that brings things together, intervened.

Dark matter doesn't talk to radiation,

doesn't talk to light.

Can do whatever it wants.

It starts clumping together.

Radiation pushes normal matter apart,

stopping it from forming dense regions.

But photons simply pass straight through the dark matter,

allowing it to clump and fall into dense pockets or wells.

The dark matter begins to clump together gravitationally,