There are various arguments for the metaphysical impossibility of time travel. Is it impossible because objects could then be in two places at once? Or is it impossible because some objects could bring about their own existence? In this book, Nikk Effingham contends that no such argument is sound and that time travel is metaphysically possible. His main focus is on the Grandfather Paradox: the position that time travel is impossible because someone could not go back in time and kill their own grandfather before he met their grandmother. In such a case, Effingham argues that the time traveller would have the ability to do the impossible (so they could kill their grandfather) even though those impossibilities will never come about (so they won't kill their grandfather). He then explores the ramifications of this view, discussing issues in probability and decision theory. The book ends by laying out the dangers of time travel and why, even though no time machines currently exist, we should pay extra special care ensuring that nothing, no matter how small or microscopic, ever travels in time.

If you are interested in time travel, then this book is an absolute must. It's packed full of great stuff. Even if you aren't particularly interested in time travel per se, this book should still be of interest. . . . All in all, there's a tonne to like about this book . . . I recommend it to young and old alike. * Kristie Miller, Notre Dame Philosophical Reviews *
...the book is well written and provides a thorough examination of the existing literature...Recommended. Upper-division undergraduates. Graduate students, faculty, and professionals. General readers. * R. M. Davis, CHOICE *

Nikk Effingham is Reader in Philosophy at the University of Birmingham. He received his doctorate from the University of Leeds and has previously worked at the University of Glasgow. His areas of research include metaphysics, philosophy of religion, and philosophy of science. Other than time travel, he has also written papers on supersubstantivalism, composition, and perdurantism.