  We conclude that, even apart from general doubts about a  probabilistic account of causation, the resort to a probabilistic  conception of time machines is a desperate stretch, at least in the  context of classical general relativity theory. In a quantum theory  of gravity, a probabilistic conception of time machines may be  appropriate if the theory itself provides the transition  probabilities between the relevant states. But an evaluation of this  prospect must wait until the theory of quantum gravity is available.