In this paper we explain why and how tachyons do not imply any causality violation within relativistic theories. Particular emphasis is given to the role of the Stückelberg-Feynman reinterpretation principle, both in ordinary physics and in tachyon physics.

It is suggested that the existence of a preferred cosmological reference frame has a number of generally unrecognized implications which are by no means inconsistent with the assumptions and consequences of special relativity. Indeed, the assumption that there exists a cosmological fundamental reference frame for light propagation leads to an intelligible interpretation of relativistic effects and of the null observations of Michelson-Morley-type experiments. Hence all such experiments are impotent for the detection of any such fundamental frame, and it is shown (...) that this applies also to the ingenious coupled-mirrors experiment proposed by S. Marinov. Only astronomical observation allied to cosmological theory can reveal the existence of this frame. (shrink)

Although the existence of tachyons is not ruled out by special relativity, it appears that causal paradoxes will arise if there are tachyons. The usual solutions to these paradoxes employ some form of the reinterpretation principle. In this paper it is argued first that the principle is incoherent, second that even if it is not, some causal paradoxes remain, and third, the most plausible “solution,” which appeals to boundary conditions of the universe, will conflict with special relativity.

It is shown that in addition to the usual difficulties related to causality, the theory of superluminal particles also exhibits paradoxical symmetry violations. In the second part of the paper a conventional paradox is revisited: causality violations at the macroscopic level follow from simple statistical arguments.

Tachyon paradoxes, including causality paradoxes, have persisted within tachyon theories and left little hope for the existence of observable tachyons. This paper presents a way to solve the causality paradoxes, along with two other paradoxes, by the introduction of an absolute frame of reference in which a tachyon effect may never precede its cause. Relativity for ordinary matter is unaffected by this, even if the tachyons couple to ordinary particles. Violations of the principle of relativity due to the absolute frame (...) would appear only in the case of free tachyons. (shrink)