  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.
