tachyon

Tachyon

A hypothetical faster-than-light particle consistent with the special theory of relativity. According to this theory, a free particle has an energy E and a momentum p which form a Lorentz four-vector. The length of this vector is a scalar, having the same value in all inertial reference frames. One writes

(1) 

Eq. (1), where c is the speed of light and the parameter m² is a property of the particle, independent of its momentum and energy. Three cases may be considered: m² may be positive, zero, or negative. The case m² > 0 applies for atoms, nuclei, and the macroscopic objects of everyday experience. The positive root m is called the rest-mass. If m² = 0, the particle is called massless. A few of these are known: the electron neutrino, the muon neutrino, the photon, and the graviton. The name tachyons (after a Greek word for swift) has been given to particles with m² < 0.

In general, the particle speed is given by Eq. (2). If m² < 0,

(2) 

Eq. (1) implies E > c p and Eq. (2) gives v < c. If m² = 0, then E = c p and v = c. In case m² < 0, one finds E < c p and v > c. Tachyons exist only at faster-than-light speeds. See Elementary particle, Relativity

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

tachyon

[′tak·ē‚än]

(particle physics)

A hypothetical particle that travels faster than light, consistent with the theory of relativity.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.