There is No Time Like the Present

Abstract

Abstract Throughout the many changes in basic concepts that have occurred in the recent history of physics one underlying assumption has persisted. It is the assumption that events are individuated by reference to the places and times at which they occur. There is assumed to be a manifold of spatial locations and a manifold of temporal locations. In modem physics the two independent Newtonian manifolds of spatial places and temporal moments are replaced by a single manifold of locations, each of which is a place-at-a-moment. This is the Minkowski representation. Within this representation all ‘locations’ are on an equal footing. In the Newtonian scheme the totality of places constituted the spatial manifold, which was thought to exist independently of whether places were occupied by material things, and the totality of moments, which existed independently of whether there existed events at any of the moments that constituted the manifold. The manifolds of places and of times were independent of one another in that ‘distances’, independent of choice of a particular coordinate system, could be calculated in one without reference to the other. In the Minkowski scheme the ‘three plus one’ dimensions of Newtonian physics are replaced by a four dimensional manifold intended as a model coordinate system for representing places-at-times. In this scheme, the measure of the Newtonian intervals, whether of space or of time, changes with choice of coordinate system and reference frame. The only frame-independent measure in Minkowski space-time is the separation of events considered as located at places-at-times.