Superluminal Signalling, Preferred Frames, and the Tachyonic Antitelephone

The tachyonic antitelephone is commonly cited as evidence that superluminalsignalling is fundamentally incompatible with relativistic causality.This conclusion, however, relies on the assumption that superluminalsignal velocities are defined locally in the rest frame of each emitter. Inthis paper we demonstrate that causal paradoxes are not inevitable. Wefirst review the standard Tolman antitelephone and reproduce a closedcausal loop using an explicit numerical example. We then reconsider theidentical kinematical setup under the assumption that superluminal propagationis anchored to a single physically distinguished inertial frame. Motivatedby cosmology, we take this frame to be the cosmological rest frame,which provides a natural cosmic time parameter. Under this assumption,all signal exchanges remain causally ordered and closed causal loops areexcluded. The analysis clarifies the precise origin of the antitelephoneparadox and shows that it arises from enforcing the relativity principle onsuperluminal propagation rather than from superluminal signalling itself.