The passing of time

One of the difficulties of talking sense about time travel is that it means different things to different people. For some it means the ineluctable passing of time, while for others it means the exotic activities of time travellers such as Dr Who. Yet, although these are different, they are not unrelated, and to talk sense about the latter I must first say something about the former.

The sense in which we all travel in time is the sense in which time passes, as it always has and always will. If that is time travel, there is no doubt that it occurs, and occurs automatically. In this sense we have no choice but to travel in time: it is not something we can choose to do, more or less easily. It just happens to us, as to everything else, whether we like it or not.

The main problem posed by time passing is how to make sense of it passing more or less quickly, as it often seems to do. The best way to see the problem is to compare the rate at which it passes with the rates at which other changes occur, as when space passes by a train taking an hour to cover the 60 miles from London to Cambridge. During that journey, space is passing at a mile a minute, a rate that is both objective and variable, since the train could go either faster or slower.