One of the most striking characteristics of general relativity, Einstein’s geometric theory of gravitation, is that time does not appear in it as a dynamic variable: the theory describes the evolution within a block of space-time through which embedded observers perceive events occurring in different orders depending upon their state of motion and thus have different perceived pasts and futures. (The theory does, however, strictly preserve causality, in that two events which can be connected by the path of a photon (null geodesic) are always observed as occurring in the same order by all observers.
This “block universe”, which philosophers call “eternalism”, seems deeply at variance with our perception of time and assumption of free will. But the theory works, has withstood more than a century of experimental tests, and predicted numerous novel phenomena which were subsequently observed as occurring. Should we take the block universe more seriously, or is there another way to reconcile our perception of time with the way the universe appears to work?