Causality and Space-like Signals

Abstract

ALTHOUGH we pointed out1 in 1962 that space-like particles (signals) travelling “backward in time” carry negative energy—or must be reinterpreted—recent textbooks on the special theory of relativity (for example, refs. 2–7) still purport to show that causality arguments forbid the existence of faster-than-light particles. One book which is at least partially correct on this score is Ya. P. Terletskii's Paradoxes in the Theory of Relativity8, but even this ignores the possibility of reinterpretation.