Spreading time through space: An analysis of the conventionality of intra-frame simultaneity.

Abstract

It is shown that the simultaneity of distant events is taken for granted by some major thinkers, most notably Leibniz and Newton, preceding Einstein. However, in 1905, the STR's examination, and subsequent reconstruction, of this assumption, engendered two types of simultaneity: intra-frame and inter-frame. The former is the focus of this investigation and deals with the simultaneity of distant, yet relatively stationary, events. The latter involves the simultaneity of distant, yet relatively moving, events. Einstein glossed over the former, briefly claiming that distant clocks are synchronized according to a definition. Reichenbach interpreted this as illustrating that the STR supports a conventionalist reading. The synchronization of distant clocks within the same inertial frame is only possible according to a convention. This is known as the conventionality of simultaneity, not to be confused with the relativity of simultaneity which deals with the setting of clocks in different inertial frames. Grunbaum follows Reichenbach's view and argues further that inter-frame relativity of simultaneity must be understood on the basis of intra-frame conventionality of simultaneity. It is argued that Grunbaum occupies a middle position between the two major approaches to the philosophy of space-time. Grunbaum's defence of the conventionality of simultaneity is the main concern of this investigation. Reichenbach's a priori, inter-theoretical conventionalism is clearly separated from Grunbaum's a posteriori, intra-theoretical conventionalism. This is done because the two thinkers are often misleadingly equated. They are linked simply because a particular argument, which connects conventionality and light signals, is shared. The moral of this chapter is not only that shared conclusions do not entail shared premises, but more importantly, shared arguments do not entail shared approaches. (Abstract shortened by UMI.)