Also found in: Dictionary, Wikipedia.


(tăk`ēŏn'), hypothetical elementary particleelementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
..... Click the link for more information.
 that travels only at speeds exceeding that of light. According to the theory of relativityrelativity,
physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference.
..... Click the link for more information.
, the speed of light is the limiting velocity for all ordinary material particles. Particles having nonzero rest mass can approach, but not reach, the speed of light, since their mass would become infinite at that speed. On the other hand, particles with zero rest mass, such as the photonphoton
, the particle composing light and other forms of electromagnetic radiation, sometimes called light quantum. The photon has no charge and no mass. About the beginning of the 20th cent.
..... Click the link for more information.
, must always travel at the speed of light; they cannot be brought to rest or even slowed down. Theorists have argued that since nothing in principle prohibits the existence of a third class of particles that travel only at speeds exceeding that of light, such particles, called tachyons [Gr. tachys,=swift] may exist although no evidence for them has been found. In the terminology of the theory, the particles that travel only at the speed of light are called luxons, and those that travel at lesser speeds are called tardyons. Like the original theory of relativity, the theory of tachyons has several aspects that appear to contradict common sense but that are fully self-consistent. For example, a tachyon must have an imaginary (in the mathematical sense) rest mass, or proper mass, and it must travel faster rather than slow down when it loses energy.


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

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,

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


(particle physics)
A hypothetical particle that travels faster than light, consistent with the theory of relativity.
References in periodicals archive ?
Rice Advanced Engineering Systems and Research, a California-based start-up, is planning to produce a 1,200bhp model called the Tachyon Speed.
As the Tachyon product is absorbed into Samsung KNOX [TM], 202 Partners will continue to assist Kaprica Security with its next generation vehicle cybersecurity product, RunSafe Security.
Felly, roedd pob amser cinio, ein hamser ar ol ysgol a'n holl ddyddiau Sul yn gorfod cael eu treulio yn gweithio ar Tachyon eto.
Encouraged by their Design and Technology teachers Team Tachyon had to design, construct and race the fastest Formula One car of the future, powered by compressed air cylinders.
Multiple industry standard SI and thermal TVs have been built successfully with Tachyon.
Tachyon FMO has been demonstrated on customer cases to reduce tapeout cycle time by over 65%, compared to using advanced techniques for the entire chip.
THE COMPETITION: A year after Tachyon launched its web transliteration tool, Google responded with Indic.
Although represented by only five crops of racing age, Agnes Tachyon is the sire of 17 stakes winners, including champions Daiwa Scarlet, winner of last season's Arima Kinen, Deep Sky, winner of the Japanese Derby, and Little Amapola, winner of the Queen
The Tachyon is capable of providing real-time data connectivity, Voice-over-IP and video teleconferencing.
When Johnny and Kirsty visit Mrs Tachyon in hospital, she tells them her trolley is special - or at least, the bags are.
A Tachyon setup could relay surveillance video from sites that we need to monitor live," said Wesley Fox, special agent in the NCIS' technical services division.