88:3 July 2005
Time Travel 

Advisory Editor: Achille Varzi, Columbia University

Might we some day be in a position to move about in time, just as we can already move about in space? Few would question that deliberate change in temporal location is logically possible. But is it also metaphysically possible? Is there a possible world in which one might freely change one's location in time? Here is where puzzlement and bewilderment lead to philosophical controversy. Someone traveling into the past could shoot her grandfather's identical twin but not her own grandfather. Someone traveling from the future could help you win your next game of poker, but not the one you have just lost. To some philosophers asymmetries such as these must be unacceptable, and so they conclude that time travel is impossible, physically as well as metaphysically. To others the paradoxes of time travel are only apparent. Time travel would be peculiar, to be sure, but not absurd; it would be strange, but not impossible.

Quarrels on these matters are gaining new interest today as a result of recent work in cosmology and on the theory of causation. They bear also on recent discussions of the problems of free will and personal identity. The present number of The Monist aims to promote further progress in this debate, with emphasis on questions such as the following. Would travel to the past require reverse causation? Would travel to the future entail determinism? Is the apparent asymmetry between a fixed past and an open future merely an epistemic illusion? Does the possibility of time travel entail a realist attitude toward past and future facts? Does it entail commitment to entities that do not presently exist? Does it entail that things may be wholly present in several places at once?

Table of Contents:

Achille C. Varzi

Foreword

Theodore Sider

Traveling in A- and B- Time

Robin Le Poidevin

The Cheshire Cat Problem and Other Spatial Obstacles to Backwards Time Travel

Jonathan Simon

Is Time Travel a Problem for the Three-Dimensionalist?

Matthew Slater

The Necessity of Time Travel (on Pain of Indeterminacy)

Nicholas J.J. Smith

Why Would Time Travellers Try to Kill their Younger Selves?

Peter Vranas

Do Cry Over Spilt Milk: Possibly You Can Change the Past

Steven Savitt

Time Travel and Becoming

David Horacek

Time Travel in Indeterministic Worlds

Gordon Stevenson

Time Travel, Agency, and Nomic Constraint