Outlawing time machines

chronology protection theorems

John Earman

pp. 5-19

in: Ulrich Majer, Heinz-Jürgen Schmidt (eds), Reflections on spacetime, Berlin, Springer, 1995

Abstract

At the outset I want to distinguish between two questions which are often run together: (1) Is time travel possible? and (2) Is it possible to operate a time machine? Each question can be treated in various contexts. The context I will explore here is provided by the classical form of the general theory of relativity (GTR), although towards the end I will make some remarks about the implications of quantum theory and quantum gravity.