Causality and Tachyons

Abstract

IN a recent article in Nature, Bilaniuk and Sudarshan¹ attack textbooks on the special theory of relativity which “still purport to show that causality arguments forbid the existence of faster-than-light particles” despite their demonstration^2–4 that particles going backward in time can be reinterpreted as antiparticles going forward in time. The causality argument is, however, strong, and does not seem to have been overcome by these authors. It is worth restating the argument in a simple form so that it can be seen what properties a particle travelling faster than light must have if it is not to violate the principle that a cause must precede an effect.