Time is the Simplest (and Strongest) Thing

Abstract

What is the difference between time and space? This paper proposes an answer: the temporal direction is that direction on the manifold of events in which our best theories can tell the strongest, most informative "stories." Put another way, time is that direction in which our theories can obtain as much determinism as possible. I make two arguments. The first is a general one defending the idea that strength determines what is temporal. The second is a more specific technical illustration of the first: understanding 'strength' as having a well-posed Cauchy problem, I show that for a wide class of equations, namely, linear second-order partial differential equations, the desire for strength does indeed distinguish the temporal direction. After assessing how general the second argument is, the paper explores the ramifications of this theory for various problems in the philosophy of time.