Julie Freeman, age 14, of Gastonia, N.C., for her question:

WHAT IS A TACHYON?

A tachyon is an atomic particle that exists only in theory. If one did exist in nature, it would never stand still but would always move at speeds greater than the speed of light (186,282 miles per second).

Tachyon comes from the Greek word for swift.

According to the special theory of relativity, ordinary matter can move only at speeds less than the speed of light. Albert Einstein, the great German¬American physicist, published the special theory of relativity in 1905. In 1962 several physicists found new solutions to the mathematical equations of Einstein's theory. The new solutions provided a mechanical description of the tachyon. However, no scientific experiment has ever found any evidence of a tachyon.