Reconsidering Relativistic Causality

TL;DR

This paper examines the complex and sometimes problematic nature of relativistic causality in quantum physics, highlighting scenarios where causal signals may appear to violate light-cone constraints and emphasizing the importance of physical context in geometric interpretation.

Contribution

It introduces and analyzes unfamiliar scenarios like the Drummond-Hathrell and Scharnhorst effects, challenging assumptions about relativistic causality in quantum physics.

Findings

Drummond-Hathrell effect suggests possible superluminal photon propagation.

Scharnhorst effect indicates light speed can be slightly increased in certain conditions.

Familiar scenarios like pilot-wave and Newton-Wigner are also discussed.

Abstract

I discuss the idea of relativistic causality, i.e. the requirement that causal processes or signals can propagate only within the light-cone. After briefly locating this requirement in the philosophy of causation, my main aim is to draw philosophers' attention to the fact that it is subtle, indeed problematic, in relativistic quantum physics: there are scenarios in which it seems to fail. I consign to an Appendix two such scenarios, which are familiar to philosophers of physics: the pilot-wave approach, and the Newton-Wigner representation. I instead stress two unfamiliar scenarios: the Drummond-Hathrell and Scharnhorst effects. These effects also illustrate a general moral in the philosophy of geometry: that the mathematical structures, especially the metric tensor, that represent geometry get their geometric significance by dint of detailed physical arguments.