There are various arguments for the metaphysical impossibility of time travel, e.g. it’s impossible because objects could then be in two places at once, or it’s impossible because some objects could bring about their own existence. This book argues that no such argument is sound and that time travel is metaphysically possible. The main focus is on the Grandfather Paradox: if someone could go back in time, they could (impossibly!) kill their own grandfather before he met their grandmother, thus time travel is impossible. This book argues that, in such a case, 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). The remainder of the book explores the ramifications of this view, discussing issues in probability and decision theory. It ends by laying out the dangers of time travel and why, even though no time machines currently exist, we should pay extra special care to ensure that nothing, no matter how small or microscopic, ever travels in time.
From superluminal velocity to time machines?
