Can a Soufflé Rise Twice? Van Inwagen's Irresponsible Time-Travelers

If physicists send a particle or two back in time, I fear they will make snide remarks about philosophers in their armchairs claiming to know 'a priori' that this is impossible. Peter van Inwagen's account (in this volume) of 'non-Ludovician time-travel', hereafter referred to as 'VIT travel', should forestall that criticism by providing an interpretation of what the physicists will have done, and why, if his interpretation is correct, it is irresponsible. It might seem, therefore, to be quibbling for me to argue that VIT travel should be redescribed as a variant on the branching time hypothesis, according to which "time-travellers" cause there to be a new branch of time (or more accurately a new branch of 4-space) when they get out of their machines. In this chapter I first explain why this is not a mere quibble. Then I argue for the redescription thesis. Finally I anticipate objections.