TACHYONS

A tachyon is a hypothetical subatomic particle whose velocity always exceeds that of light. The existence of the tachyon, though not experimentally established, appears consistent with the theory of relativity which was originally thought to apply only to particles traveling at or less than the speed of light. Most physicists believe that faster-than-light particles cannot exist because they are not consistent with the known laws of physics. If such particles did exist and could send signals faster than light, then according to the theory of relativity they would violate causality, leading to logical paradoxes such as the grandfather paradox. Tachyons would also exhibit the unusual property of increasing in speed as their energy decreases, and would require infinite energy to slow down to the speed of light. Because a tachyon would always travel faster than light, it would not be possible to see it approaching. After a tachyon has passed nearby, an observer would be able to see two images of it approaching and departing in opposite directions. No experimental evidence for the existence of tachyons has been found.