  The thesis that the choice of standard synchrony is a convention, rather than one necessitated by facts about the physical universe (within the framework of the special theory of relativity), has been argued particularly by Reichenbach (see, for example, Reichenbach 1958, 123–135) and Grünbaum (see, for example, Grünbaum 1973, 342–368). They argue that the only nonconventional basis for claiming that two distinct events are not simultaneous would be the possibility of a causal influence connecting the events. In the pre-Einsteinian view of the universe, there was no reason to rule out the possibility of arbitrarily fast causal influences, which would then be able to single out a unique event at A that would be simultaneous with E. In an Einsteinian universe, however, no causal influence can travel faster than the speed of light in vacuum, so from the point of view of Reichenbach and Grünbaum, any event at A whose time of occurrence is in the open interval between t1 and t2 could be defined to be simultaneous with E. In terms of the ε-notation introduced by Reichenbach, any event at A occurring at a time t1 + ε(t2 − t1), where 0 &lt; ε &lt; 1, could be simultaneous with E. That is, the conventionality thesis asserts that any particular choice of ε within its stated range is a matter of convention, including the choice ε=1/2 (which corresponds to standard synchrony). If ε differs from 1/2, the one-way speeds of a light ray would differ (in an ε-dependent fashion) on the two segments of its round-trip journey between A and B. If, more generally, we consider light traveling on an arbitrary closed path in three-dimensional space, then (as shown by Minguzzi 2002, 155–156) the freedom of choice in the one-way speeds of light amounts to the choice of an arbitrary scalar field (although two scalar fields that differ only by an additive constant would give the same assignment of one-way speeds).