What happened to antimatter? - Rolf Landua

Translator: Andrea McDonough Reviewer: Jessica Ruby

Is it possible to create something out of nothing?

Or, more precisely, can energy be made into matter?

Yes, but only when it comes together

with its twin, antimatter.

And there's something pretty mysterious about antimatter:

there's way less of it out there than there should be.

Let's start with the most famous physics formula ever:

E equals m c squared.

It basically says that mass is concentrated energy,

and mass and energy are exchangeable,

like two currencies with a huge exchange rate.

90 trillion Joules of energy

are equivalent to 1 gram of mass.

But how do I actually transform energy into matter?

The magic word is <i>energy density</i>.

If you concentrate a huge amount

of energy in a tiny space,

new particles will come into existence.

If we look closer,

we see that these particles always come in pairs,

like twins.

That's because particles always have a counterpart,

an antiparticle,

and these are always produced

in exactly equal amounts: 50/50.

This might sound like science fiction,

but it's the daily life of particle accelerators.

In the collisions between two protons

at CERN's Large Hadron Collider,

billions of particles and antiparticles

are produced every second.

Consider, for example, the electron.

It has a very small mass and negative electric charge.

It's antiparticle, the positron,

has exactly the same mass,

but a positive electric charge.

But, apart from the opposite charges,

both particles are identical and perfectly stable.

And the same is true for their heavy cousins,

the proton and the antiproton.

Therefore, scientists are convinced

that a world made of antimatter

would look, feel, and smell just like our world.

In this antiworld,

we may find antiwater,

antigold,

and, for example,

an antimarble.

Now imagine that a marble and an antimarble

are brought together.

These two apparently solid objects

would completely disappear

into a big flash of energy,

equivalent to an atomic bomb.

Because combining matter and antimatter

would create so much energy,

science fiction is full of ideas

about harnessing the energy stored in antimatter,

for example, to fuel spaceships like Star Trek.

After all, the energy content of antimatter

is a billion times higher than conventional fuel.

The energy of one gram of antimatter would be enough

for driving a car 1,000 times around the Earth,

or to bring the space shuttle into orbit.

So why don't we use antimatter for energy production?

Well, antimatter isn't just sitting around,

ready for us to harvest.

We have to make antimatter

before we can combust antimatter,

and it takes a billion times more energy

to make antimatter

than you get back.

But, what if there was some antimatter in outer space

and we could dig it out one day

from an antiplanet somewhere.

A few decades ago, many scientists believed

that this could actually be possible.

Today, observations have shown

that there is no significant amount of antimatter

anywhere in the visible universe,

which is weird because, like we said before,

there should be just as much antimatter

as there is matter in the universe.

Since antiparticles and particles

should exist in equal numbers,

this missing antimatter?

Now that is a real mystery.

To understand what might be happening,

we must go back to the Big Bang.

In the instant the universe was created,

a huge amount of energy was transformed into mass,

and our initial universe contained

equal amounts of matter and antimatter.

But just a second later,

most matter and all of the antimatter

had destroyed one another,

producing an enormous amount of radiation

that can still be observed today.

Just about 100 millionths

of the original amount of matter stuck around

and no antimatter whatsoever.

"Now, wait!" you might say,

"Why did all the antimatter disappear

and only matter was left?"

It seems that we were somehow lucky

that a tiny asymmetry exists

between matter and antimatter.

Otherwise, there would be no particles at all

anywhere in the universe

and also no human beings.

But what causes this asymmetry?

Experiments at CERN are trying to find out the reason

why something exists

and why we don't live in a universe

filled with radiation only?

But, so far, we just don't know the answer.