During their search for different particles scientists found some
particles which had exactly the same properties as the particles already known,
except that they had opposite charges. They named these particles antiparticles.
It was found that every known particle has its corresponding antiparticle. So for an
up quark there is an anti up quark and for an electron you have the anti electron.
Our world is primarily made up of matter, not antimatter. This is a good thing since
there's a little catch to antiparticles. Every time a particle hits a corresponding
antiparticle, they annihilate, which means as much as that they dissapear into a flash of
energy. In reverse, particles and their antiparticles are created
from energy all the time.
The annihilation and creation of matter and antimatter is one of the greatest phenomena to make
theories about. One of the most fascinating theories is that
particles and antiparticles are exactly the same thing, except that matter goes "forwards" in
time while antimatter goes the other way.
You can see this theory illustrated in the animation on the left. The black arrow at the top
shows the passing of time. Beneath it you can see how a down quark hits a photon (an energy particle)
and is hurled back in time. If you click on "animated" you can see what this illustrated event
looks like to us when time is passing. And there you have your annihilation. Click on "creation"
to see the process of creation of particles and antiparticles.
If matter and antimatter are created and annihilated all the time, you will soon ask the question
why there seems to be so little antimatter in our world. There are different theories about
this aspect of antimatter. Some people think that there is a slight difference between
matter and antimatter so that there's a small chance that not all matter is destroyed.
Another theory is that there are whole planets, galaxies, or even universes
made from antimatter. It would be interesting to meet a creature from such a planet...