A panel discussion of simultaneity by slow clock transport in the special and general theories of relativity

pp. 666-708

in: Adolf Grünbaum, Philosophical problems of space and time, Berlin, Springer, 1973

Abstract

In his famous 1905 paper on the special theory of relativity (STR), before the subject of the relativity of simultaneity in systems in relative motion is even broached, Einstein enunciates explicitly his doctrine of the definitional character of simultaneity in a single 'stationary" system ([2], p. 40). Subsequent interpreters, most notably Reichenbach, have maintained that Einstein was correctly claiming the relation of simultaneity in a single inertial system to be conventional in a significant and nontrivial sense ([4], p. 127). Einstein there describes a method of synchronizing clocks located at different places in the stationary system by a signalling process. Suppose two clocks U _A and U _B are located at places A and B respectively. Let a light signal be sent from A to B, where it is immediately reflected back to A. Let t ₁ be the time at which the signal departs from A, and let t ₃ be the time of its return to A after reflection at B, both times measured on U _A. Einstein establishes a synchrony between U _A and U _B by stipulating that the time taken for the signal to travel from A to B equals the time it takes to return from B to A.