A particle which always moves faster than the speed of light. Such particles are hypothetically possible, but none has ever been observed, and their actual physical existence is now considered more than a little doubtful. Also see luxon and tardyon.

a hypothetical faster-than-light quantum particle, which has not been proven to actually exist

a hypothetical particle that travels at superluminal velocities

a hypothetical particle that travels faster than the speed of light and has imaginary mass

a theoretical particle that always travels faster than light

a theoretical particle that can travel faster than the speed of light

a type of subatomic particle that exists only at faster-than-light velocities

a [theoretical] particle that moves faster than light.

A tachyon (from the Greek (takhús), meaning "swift, fast") is any hypothetical particle that travels at superluminal velocity. The first description of tachyons is attributed to German physicist Arnold Sommerfeld, but it was George Sudarshan, Olexa-Myron Bilaniuk and Gerald Feinberg (who originally coined the term) in the 1960s who advanced a theoretical framework for their study. Tachyons have recurred in a variety of contexts, such as string theory.