How do we know it is now now?

Abstract

Many philosophers have found a theory of time that shares features of four dimensionalism with an account of the genuine passage of time to be attractive. C. D. Broad (1923), Michael Tooley (1997) and Peter Forrest (forthcoming), for example, defend a view that has at least these features in common. The future is unreal: it does not exist. The past however does exist it is a space-time volume of the kind that orthodox four dimensionalists think that the universe is as a Parmenidean whole. The present is a kind of hyperplane that borders reality; it is the edge of Being. As time goes on, the volume of the universe increases. Think of it as a kind of (four-dimensional) growing salami. The universe starts out with a single slice, and as time moves on slices are progressively added to it. Such a view shares with any genuine passage of time view difficulties in understanding in what dimension the change happens (Smart 1964, 1980; Griinbaum 1973); it seems there are two kinds of time: time understood as location in the four dimensional manifold that is the present and past, and objective time which tells you where the border is. This second kind of time seems to need another, problematic dimension to move in. There are various solutions to such problems (Markosian 1993; McCall 1994), and I think that the jury is out on whether genuine passage is coherent. But there is a problem with the growing salami view that seems insuperable. I argue that on the growing salami view, it is almost certainly not now. It is not now now; or less tendentiously, the current time is probably not the present. What do other theories of time tell us about how we know that the