Tachyon

Tachyon, subatomic particles that in theory move faster than the speed of light. According to Albert Einstein's theory of relativity (1905), all matter moves slower than the speed of light (186,282 mi per sec/299,792 km per sec). Theoretically, tachyons gain energy as they slow down; it would take massive amounts of energy to slow them down to approximately the speed of light. Physicists today believe that the existence of tachyons fits into Einstein's theory, even though experiments have not as yet proved their existence.