Causal paradoxes: a conflict between relativity and the arrow of time

TL;DR

This paper discusses how causal paradoxes in relativity arise from confusing the relativistic coordinate time with the thermodynamic arrow of time, proposing that the latter resolves these paradoxes.

Contribution

It clarifies that the true physical arrow of time is thermodynamic, not relativistic, resolving apparent causal paradoxes in relativity.

Findings

Causal paradoxes result from misidentifying the time arrow.

Thermodynamic arrow of time is absolute and irrotational.

Relativistic coordinate time does not define causality.

Abstract

It is often argued that superluminal velocities and nontrivial spacetime topologies, allowed by the theory of relativity, may lead to causal paradoxes. By emphasizing that the notion of causality assumes the existence of a time arrow (TA) that points from the past to the future, the apparent paradoxes appear to be an artefact of the wrong tacit assumption that the relativistic coordinate TA coincides with the physical TA. The latter should be identified with the thermodynamic TA, which, by being absolute and irrotational, does not lead to paradoxes.