there, at the edge of a black hole, or inside an exploding star.

But some of them surround us, all the time.

I can show you.

In this container, we're going to catch some super-fast subatomic particles that are

raining down on us from space.

They're called cosmic rays.

And exactly where some of them come from is part of this 100-year-old mystery in physics.

Cosmic rays are a form of radiation.

“Rays” is a misnomer — they're actually little bits of atoms whizzing by us, even

through us, all the time.

Every square centimeter of Earth at sea level, including the space at the top of your head,

gets hit by one of these particles every minute.

We can't feel them, and they don't cause our bodies any harm,

But they can, sometimes, do weird things: Like make computers malfunction by messing

with their memory.

Scientists have been studying cosmic rays since the early 1900s, when a physicist went

up in a hot air balloon and discovered the radiation increases the higher you go — meaning

that it comes from somewhere in space.

Since then, they've found out ways to make these little bits of atoms visible — like

we're gonna do here.

We've built something called a cloud chamber.

Up here is felt that we've soaked with a super-concentrated solution of rubbing alcohol.

And at the bottom here is dry ice which is super cold.

So when the alcohol vapor goes down to the bottom and gets really cold — it condenses

and forms a cloud.

And when the cosmic rays come shooting in from space — the alcohol vapor forms into

little droplets and you can actually trace their path through the cloud.

Hopefully.

Okay, let's look.

Wait!

I saw one!

Yeah!

The particles in our cloud chamber are traveling from space at nearly the speed of light, as

are the untold others passing by you and through you right now.

When they hit our atmosphere, the impact is so powerful that the atoms of radiation burst

open — tearing apart in violent, cascading collisions.

That's what we see in the cloud chamber: atomic shrapnel that has reached the ground.

Scientists have determined that some of these rays come from the sun's atmosphere, in

the form of solar wind, and others from exploding stars.

But the most powerful rays are the most puzzling — they don't even come from our own galaxy.

They come from some unknown source out in the universe.

The energy from the very most powerful ray recorded had enough power to turn on a light

bulb for a second or more.

That force is comparable to a top tennis pro hitting a ball with all their strength.

It doesn't sound that impressive, but think of this: all that energy is squeezed into

an area smaller than an atom.

To try to figure out what entity could be shooting these incredibly powerful rays at

us, scientists use massive cosmic ray observatories, with detectors not too different from our

cloud chamber.

Well… you know, they're on a higher budget and they're more advanced.

One in the South Pole uses a block of ice, a whole cubic kilometer, to track the rays

instead of vapor.

Another one in Argentina has 1,600 huge water tanks, spread out over 1,000 square miles.

But instead of just observing cosmic rays as they shoot by, scientists use sophisticated

technology to trace the atomic shrapnel backward.

There, they can reconstruct the original cosmic ray that hit at the top of the atmosphere.

But confirming their source in the deep reaches of space isn't so easy, because these cosmic

rays don't always travel in a straight line.

Instead, the various magnetic fields of the universe and the galaxy, put them on

bendy paths.

Scientists have a few suggestions.

The cosmic rays could be created in the violent hearts of galaxies far away.

Another leading hypothesis is that they're not produced by exploding stars, per se, but

by bouncing around the shockwaves produced by those explosions.

There is also the possibility that some of the rays are produced by forces and objects

we don't know about — or interact with things like dark matter, in ways we don't

yet understand.

Or they could come from strange objects left over from the big bang.

I mean aliens could be shooting these at us… but I doubt it.

What scientists need is more data, more observations to be able to pinpoint the sources in the

sky these particles are coming from.

If scientists can figure out where the most

powerful cosmic rays come from, it means they're discovering one of the most powerful things

in the entire universe.

Perhaps the most powerful thing in the entire universe.

That might open up an entirely new branch of physics, teaching us about how the universe

was formed, and about how matter can be pushed to the extreme.

But until their origin is discovered, we can think of cosmic rays as messengers from the

broader universe.

A reminder we're a part of it, and that there's still a great deal of mystery out

there.