Faster than light travel and time machines are among the most tantalising possibilities allowed for by Einstein’s general relativity. In this chapter we shall review the main features of these phenomena, in which spacetimes they appear to be realised, and explain why they are interconnected with the Einsteinian framework. We shall then discuss briefly the paradoxes related to the possibility of time travel and the proposed solutions. Finally, we shall provide an explicit example where a purely semiclassical gravity framework seems sufficient to prevent the stability of a spacetime allowing faster than light propagation. We shall argue that this lends support to a sort of “pre-emptive” chronology protection that forbids the generation of the very spacetime structures which could lead to the construction of time machines.
