A Beginner's Guide to Antimatter

It may be the ultimate fuel for space travel, but right now antimatter is fleeting, difficult to work with, and measured in atoms not pounds!

What do you think of when you hear the word "antimatter?" Something exotic, something unreal? Something about your Chief Engineer not being able to keep the containment fields up during battle?

Well, to a few scientists and university researchers, antimatter may just be the future of human space travel. When it comes to packing a punch, antimatter/matter reactions can't be beat. When a particle and its antiparticle meet, they annihilate each other and their entire mass is converted into pure energy.

Many physics textbooks describe matter as something "that takes up space and has mass." Every physical object that you've ever seen consists of matter. So if everything you know is made of matter, then what's antimatter? Let's go back to the 1930s to find an answer.

In 1928, the British physicist Paul A.M. Dirac (1902-1984) formulated a theory for the motion of electrons in electric and magnetic fields. Such theories had been formulated before, but what was unique about Dirac's was that his included the effects of Einstein's Special Theory of Relativity. Dirac's equations worked exceptionally well, describing many attributes of electron motion that previous equations could not.

But his theory also led to a surprising prediction that the electron must have an "antiparticle," having the same mass but a positive electrical charge (the opposite of a normal electron's negative charge). In 1932 Carl Anderson observed this new particle experimentally and it was named the "positron." This was the first known example of antimatter. In 1955 the antiproton was produced at the Berkeley Bevatron, and in 1995 scientists created the first anti-hydrogen atom at the CERN research facility in Europe by combining the anti-proton with a positron (the normal hydrogen atom consists of one proton and one electron). But when these antihydrogen atoms are produced, they are travelling at nearly the speed of light and don't last too long (40 nanoseconds is typical).

Dirac's equations predicted that all of the fundamental particles in nature must have a corresponding "antiparticle." In each case, the masses of the particle and antiparticle are identical, and other properties are nearly identical. But in all cases, the mathematical signs of some property are reversed. Antiprotons, for example, have the same mass as a proton but the opposite electric charge. Since Dirac's time, scores of these particle-antiparticle pairings have been observed. Even particles that have no electrical charge, such as the neutron, have antiparticles. These have other properties with a sign (such as magnetic moment) that can be reversed.