The long answer to "What is Antimatter" and its current uses:
Antimatter has many opposite properties to the ordinary matter we are made of. It has a long history, and yes, very small amounts of antimatter are produced routinely in particle physics laboratories every day.
The existence of antimatter was one of the early triumphs of the twentieth century theories of physics. In 1928, Paul Dirac proposed a description of electrons which combined ingredients of quantum mechanics and special relativity and which seemed to work very well. The equations had the odd feature that not only did the solutions describe electrons, but additional solutions described the behavior of particles which behaved a lot like electrons (same mass and spin, for example) but which had opposite charge. If one of these other particles ever interacted with an electron, both would disappear in a burst of energy. This seemed very crazy back in 1928, and people wondered if we should just ignore these other solutions to the equations.
Theories need to be put to the test in nature in order for the scientific method to work, and Anderson did so in 1933. In a cloud chamber, his group discovered that particles just like electrons but with a positive charge (electrons have negative charge) were found to occur naturally, and some of these positively-charged electrons rained down on Earth as a result of cosmic rays interacting with the atmosphere. The new particle was called the positron.
Since then, all particles we know about have been found to have antiparticles, and our theories of particles don't make sense without them. Some particles are their own antiparticles, for example, the photon. Antiparticles can annihilate with particles to make a burst of energy; the opposite reaction also occurs. If you put enough energy together in one place, you can produce a particle and an antiparticle pair together.
In particle accelerators, electrons or protons are accelerated to high speeds and collided with other bits of matter. In the collisions, enough energy is released to make particle-antiparticle pairs. Many accelerators are cleverly designed and can collect the antiparticles and accelerate them in turn, colliding them later with beams of particles in order to study even more interesting collisions. That's what some of us do for a living. Positrons are much easier to make than antiprotons, because they are much lighter. Many other kinds of antimatter are unstable because their matter counterparts are unstable too (i.e., they exist for a very tiny fraction of a second before decaying into more usual stuff).
One note on how little antimatter has been produced (from our answer on making antimatter for space flight
According to Gerald Gabrielse, a Harvard professor who is doing research on the production and storage of antihydrogen (a form of antimatter), even if you could collect all of the antiprotons ever made (by humans), you couldn't even heat up a cup of coffee with the energy released by annihilation.
Antimatter is opposite to matter in many ways but not all:
1) It has opposite charge
2) It can annihilate with their counterpart matter particles
But antimatter has many similarities
1) A particle and antiparticle have the same mass (as far as we can tell). So they all attract gravitationally just like real matter (no antigravity with antimatter, sorry!)
2) They have the same spin
3) Unstable antimatter particles have the same lifetimes as their matter counterparts.
There are some very slight difference between matter and antimatter which are currently under study. One of the main questions in physics today is: "If you can only produce matter and antimatter in pairs, in equal quantities, then why is there so much matter in the universe today, and so little antimatter?" Experiments today are trying to investigate the differences that can bring this about.
For a good introduction to this and other particle physics topics, and to see what's going on in the field today, check out the particle adventure
website at Lawrence Berkeley laboratories in California.
Does antimatter have effects on people and the environment?:
Well, we haven't produced enough of it to have a noticeable effect on anything large. In general, antimatter will not last long after it is produced because each particle will annihilate with a particle as soon as it comes in contact. (Sometimes a particle and an antiparticle will orbit each other for a short while before annihilating -- they are oppositely charged and hence attract electrostatically, but for the purpose of this question, matter and antimatter will annihilate into photons right away). Protons and antiprotons annihilate into other particles called pions which decay themselves into stuff like electrons, photons, muons (which decay into electrons) and neutrinos. So the effect of antimatter is the same as the effect of the radiation produced by its annihilation.
Can antimatter travel through matter?
Well, not really very well. Antiprotons and antielectrons, going slowly, will annihilate with their matter counterparts. If they have lots of energy, they can create sprays of other particles when they strike ordinary matter. In the case of electrons (or positrons), if the energy is high enough, they will create a shower of thousands of electron-positron pairs of lower energy. Eventually these slow down and annihilate. Some particles pass through matter rather easily, like neutrinos. Antineutrinos pass through matter about as easily as neutrinos (not quite the same because of the ability to interact and exchange charge with a nucleus or electron is different). Antimuons pass through matter as easily as muons -- both are found in cosmic rays. There really aren't any muons to annihilate with because they decay so quickly on their own.
Yes they sure should teach this in schools! We've known about antimatter for seventy-six years now!
(republished on 07/20/06)