n.
Hypothetical subatomic particle whose velocity is always greater than that of light.
Its existence appears consistent with the theory of relativity . Just as an ordinary particle such as an electron can exist only at speeds less than that of light, a tachyon can exist only at speeds greater than that of light. At such speeds, its mass would be real and positive. On losing energy, a tachyon accelerates; the faster it travels, the less energy it has. The existence of tachyons has not been established experimentally.