Anti-matter is the same thing as normal matter
but with opposite charge and magnetic momentum(magnetic momentum defines how the
particle alignes itself to a magnetic field just as a compass needle pooint in
some direction to a magnetic field). It's the magnetic momentum which makes
it possible for neutral charged particles(such as the neutron) to have a
anti-matter counter part. Eventhough they have the same electric charge(0) they
have the opposite magnetic momentum. (Note: Electromagnetic charge isn't the
only charge which can be reversed at anti-particles. Quarks, for example, also
have colour charge which is reversed in their anti-particles.)
Normal
matter(the things we are made up by) and anti-matter cannot meet. If one matter
and one anti-matter particle would come together, they would annihalate each
other.
SYMMETRY BREAKING
We and every thing around us seems to be
made out of matter alone. We don't observe any anti-matter laying around, why is
that? In the Big Bang there should theoreticly have been created the same amount
of matter as anti-matter. and therefor this matter and anti-matter should have
annihalated each other, leaving nothing but radiation behind, so clearly this
was not the case. But wait a minute, aren't we jumping to conclusions here?
After all, how do we know that the anti-matter didn't go lumpy and form entire
anti-matter galaxys. Well if they did we would see intense gamma radiation from
when matter and anti-matter collides like when for example an anti-matter star
explodes and throws pieces of itself out in space, that anti-matter will sooner
or later collide with matter and creating huge burst of gamma rays. And allso if
there were allot of anti-matter out there we would notice it in the constant
rain of particles that hits earth all the time, the cosmic rays. These cosmic
rays contain very few anti-particles and the anti-particles that is in it can be
explaned by particles hitting each other in space with high speeds and therby
creating anti-particles and by forms of radioactive decay. So it has to be
something else.
Anti-matter reacts to all the known forces in the exact
same way as normal matter does. Exept for the weak force, which is responsible
for differnet kinds of radioactive decay, therefor there seems to be a slight a
asymmety between matter and anti-matter. Anti-matter might decay easyer then
normal matter thereby leaving a surplus of matter in the beginning of the
universe to form our galaxys and planets. Test at the Japanes KEK and the
Amerikan SLAC accelerators might soon give us the answers.