<P> The possibility of particles moving faster than light was first proposed by O.M.P. Bilaniuk, V.K. Deshpande, and E.C.G. Sudarshan in 1962, although the term they used for it was "meta - particle". In the 1967 paper that coined the term, Gerald Feinberg proposed that tachyonic particles could be quanta of a quantum field with imaginary mass . However, it was soon realized that excitations of such imaginary mass fields do not in fact propagate faster than light, and instead represent an instability known as tachyon condensation . Nevertheless, in modern physics the term "tachyon" often refers to imaginary mass fields rather than to faster - than - light particles . Such fields have come to play a significant role in modern physics . </P> <P> The term comes from the Greek: ταχύ, tachy, meaning "rapid". The complementary particle types are called luxons (which always move at the speed of light) and bradyons (which always move slower than light); both of these particle types are known to exist . </P> <P> Despite theoretical arguments against the existence of faster - than - light particles, experiments have been conducted to search for them, but no compelling evidence of their existence has been found . </P> <P> In special relativity, a faster - than - light particle would have space - like four - momentum, in contrast to ordinary particles that have time - like four - momentum . Although in some theories the mass of tachyons is regarded as imaginary, in some modern formulations the mass is considered real, the formulas for the momentum and energy being redefined to this end . Moreover, since tachyons are constrained to the spacelike portion of the energy--momentum graph, it could not slow down to subluminal speeds . </P>

Who proved that tachyon is faster than light
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