General Relativity and the Conceivability of Time Travel

Abstract

It has been suggested by several philosophers (Lewis 1976, Putnam 1962) that many of the so-called paradoxes of backward time travel can be resolved if we conceive of the backward time traveller as having a zig-zag or N-shaped world line in spacetime. In this I am in general agreement. But there is still a problem in conceiving of backward time travel this way. In this note I will show how we can solve this problem by conceiving of backward time travel in terms of the closed time-like world lines in certain general relativistic space-times. Indeed, it has often been claimed (cf. Dwyer 1978, Godei 1949, Tipler 1974) that such world models as Godei spacetime show (or contribute to showing) that backward time travel is conceivable. Our discussion will help to make clear just why this claim is correct.