Here's everything you ever wanted to know about antimatter, but were afraid to ask. Or most of the things you kind of wondered about antimatter but didn't give that much of a crap about. Whichever.
Although antimatter sounds pleasantly futuristic, it was both predicted and proven to exist back in the 1930s. A gentleman by the name of Paul Dirac pointed out that there was no reason why matter had to be charged as it was. According to quantum theory, particles should be able exist with the same mass as the particles we regularly observe, but with the opposite charge. He dubbed these particles ‘antimatter,' presumably because he pictured these particles with not just an opposite charge, but dark eyebrows, a mustache that they could twirl, and an evil laugh.
Which is all well and good, but without a tiny CSI team collecting mustache hairs, what's the best way to detect antimatter? The answer is much the same now as it was in 1931, when the first antimatter particle was detected; magnets and cloud chambers.
A magnet can push a particle of one charge one way, and another charge the other way. The cloud chamber shows an observer what path the particle takes. A cloud chamber consists of either gas or fluid held in a very delicate state. Gas will be supersaturated; for example, if it's air it can be so pumped full of water vapor that it would normally form clouds. If it's liquid it can either be superheated or supercooled, so that it would normally form ice crystals or bubbles. Scientists keep the chamber at precise conditions. When something barrels through the chamber, even something as small as a subatomic particle, it upsets those conditions and causes bubbles or ice crystals or condensation – clouds - to form in its path. This marks the particle's path, and allows scientists to track its motion.
Protons and neutrons, because of their mass, travel a straighter path than electrons. If a particle has the size of an electron, but travels through an magnetic field like it's a proton, it's anti-matter. In 1931, something did just that, and was dubbed a positron (or antielectron), and has been joined by antiprotons and antineutrons.
Interesting; but it doesn't explain why matter-anti-matter engines should power the Starship Enterprise in its mission to explore strange new worlds, to seek out new life and new civilizations, and to boldly go where no one has gone before.
It turns out that when matter and antimatter combine, they ‘annihilate,' while giving off massive amounts of energy. A small amount of antimatter could easily propel spaceships, which would be a great deal lighter for not having to carry fuel around. It's the perfect situation.
The trouble with the idea is twofold. For one thing, this energy burst comes partly in the form of gamma rays, which tear through cells like tissue paper. But hey, as Eddie Izzard pointed out, you don't put on a red jumper and hurl yourself into space expecting safe working conditions. That can be managed. What can't be is any large amount of antimatter. Io9 has already talked about why there is more matter than antimatter in the universe. It's not possible to mine for antimatter, so it has to be made. And it's a bitch to make. A Large Hadron Collider scale of bitch to make.