How the Universe Works

Narrator: The sun, our nuclear powerhouse.

Our star, its light powers our world... and us.

Without light, we would not be alive.

Narrator: Starting deep inside the sun,

we follow the brutal journey

of a single, tiny package of light... a photon.

The ride that any photon takes to get to my eyes

when I look up at the sun is an amazing one.

Narrator: From its ancient birth in the sun's core.

To its escape from the surface.

Thaller: The light reaching me from the sun.

Was produced before there was even human civilization.

It's an incredible idea.

Narrator: Join our photon.

On its incredible million-year journey

through the most hostile environment in the solar system

to bring light and life to earth.

The universe, home to billions of galaxies...

Each made of billions of stars.

And, in an unremarkable corner of our galaxy, the milky way,

lies the sun, our closest star...

A dazzling sphere of intense light,

too bright for the naked eye.

But strip away that glare, and the sun transforms

into a giant ball

of super heated gas dominating our cosmic stage.

Gilbert: The sun is really the star of the show.

The sun is the parent of the whole solar system.

It provides its children, the planets,

with everything they need.

We depend on the sun for energy, for light, for warmth.

We would not exist without the sun.

Narrator: The sun generates heat and light,

the energy source for all life on earth.

Thaller: All of the energy that my body uses,

literally what I'm doing to talk to you right now,

came from the sun.

The sun truly is the creator of all of the life around us.

Narrator: The sun is a constantly exploding.

Nuclear bomb, violent and essential.

Krauss: Our entire existence is powered by the energy.

Emitted in those nuclear reactions in the sun.

We are here because of the light from the sun.

We are here because of those nuclear reactions,

and no aspect of our existence could persist

if it wasn't there.

Narrator: Light is one of the basic building blocks.

Of the universe.

Gilbert: I find light to be probably.

The most amazing thing in the universe.

It's so important in everything.

I mean, it's everything. It's everywhere.

So, it's such a fundamental part of everything that exists.

Narrator: Fundamental and fast.

The fastest thing in the cosmos...

Traveling at 186,000 miles per second.

The sun is about 93 million miles away from us.

So, going at 186,000 miles per second,

that's about eight minutes.

Narrator: But those eight minutes.

Are just the brief last leg of its incredible journey.

It may have taken the light as much as a million years

to escape from the sun's raging interior...

Which means the light we're seeing right now

was created long before

our ancestors left the plains of Africa.

Krauss: When I first learned this fact,

I was already a practicing scientist.

I had never really thought about that,

and on first glance, it just blew me away.

Thaller: Right now the light reaching me from the sun.

Was produced before there was even human civilization.

And yet, the minute it gets to the surface of the sun,

it races away and is here eight minutes after that.

It's an incredible idea.

The ride that any photon takes to get to my eyes

when I look up at the sun is an amazing one.

Narrator: That ride starts deep in the belly of our star.

If we could open up the sun,

we'd see layers of dense hydrogen gas

hundreds of thousands of miles deep.

And at its center, the core, the sun gives birth to light...

Forged in one of the most violent reactions

in the universe, nuclear fusion.

The specific nuclear reaction that powers the sun is fusion,

fusion of hydrogen into helium.

You take two hydrogen atoms, you ram them together,

and what's left over is a helium atom.

Narrator: It sounds simple enough,

but it's not.

It's actually hard to get two atoms to fuse.

Two photons have the same charge.

They're both positively charged. They want to repel each other.

Krauss: Protons don't like to get close together.

They have to come together with a huge amount

of energy or velocity

to get close enough to begin to fuse,

and that's very, very rare.

Narrator: To force protons together.

Takes immense amounts of heat and pressure...

Generated by the invisible hand of gravity.

The sun contains 99.8% of all the matter

in the solar system.

That's a lot of mass.

All that mass pulls the sun together

with unimaginable gravitational force.

Thaller: With gravity crushing things down,

things get close enough together and nuclear fusion happens.

Narrator: In this nuclear compactor,

hydrogen atoms slam together

100 million quadrillion quadrillion times each second.

Some of these collisions are so powerful that atoms fuse,

releasing energy.

When the protons come together to bind together,

they lose a little bit of mass,

and that mass gets converted into energy.

And every second of every day,

about five million tons of stuff is being converted to energy.

It's amazing.

Narrator: Each collision creates a tiny burst of energy,

a packet of light impossibly small and incredibly powerful.

Somehow, our photon will deliver its energy to earth

where it will power the planet and make life possible.

But right now it's nothing like the light we see.

It has massive amounts of energy, and it's deadly.

Narrator: The light we see from our star is old...

Much older than the eight minutes it takes

to get from the sun to earth.

That short leap across space is the end of a long, hard journey

that starts deep inside our sun.

Kaku: When we look at the sun,

we say, 'how beautiful, how elegant, and how simple.'

Light is formed in the sun,

and it shines and lights up our world.

Well, not so fast.

It's actually very complex.

Narrator: The journey starts.

In the immense heat of the sun's core.

Crushed together by the sun's enormous gravity,

atoms smash into each other and fuse...

Releasing a tiny packet of energy, photon of light...

Far smaller than an atom with no mass.

Photons travel faster than anything else,

and they never stop moving.

Photons don't just come from the core of stars.

Oluseyi: So, where does light come from?

The short answer is, matter makes it,

and the amount of light that it creates

depends on its temperature.

Narrator: Every piece of matter in the universe.

Above absolute zero degrees

produces light, including humans.

Filippenko: We humans are emitting light all the time.

Because we're alive, we're warm, we're not at a zero temperature.

So, in fact we are emitting infrared radiation,

often called heat radiation.

But all matter emits light.

Even someone as cool as me, I'm creating light right now.

Narrator: The light we see.

Can be split into the colors of the rainbow.

Each color is photons of light

with slightly different amounts of energy.

And what we can see

is only a fraction of the light spectrum.

Our eyes are actually imperfect detectors.

We know about visible light,

the type of light that our eyes are sensitive to,

but that's only a small range of energies.

Light comes at higher and lower energies than we can detect.

Narrator: Using special cameras,

we can see the infrared light that humans emit.

This infrared light

has less energy than the visible light we see.

Some light is too energetic to see,

like ultraviolets, x-rays, and gamma rays.

The vast, hot sun generates all forms of light.

But in the nuclear furnace of the sun's core,

every photon starts out as a gamma ray,

the most energetic form of light in the universe.

Krauss: And when a nuclear reaction happens,

it emits an amazing amount of energy,

the energy much, much bigger than visible light...

Gamma rays, we call them.

Literally almost a million times

or at least 10,000 times the energy of the light we see.

Narrator: Gamma rays can transform and even kill.

There's a reason why gamma rays

turned Bruce banner into the hulk.

Gamma rays are a very dangerous form of light.

They can travel into your body

and when they interact with the matter,

they can break apart atoms.

Narrator: Fortunately for us,

our gamma-ray photon can't head straight out of the sun.

Filippenko: If the sun were not this hot ball of gas,

then upon being created,

a photon would immediately escape from the sun

and it would be a gamma-ray photon,

a very energetic photon, not very good for life on earth.

Narrator: After its birth as a gamma ray,