Simultaneity, conventialism, general covariance, and the special theory of relativity

Abstract

In a recent article, De Ritis and Guccioni claimed to give an easy way of falsifying the conventionalist interpretation of the definition of simultaneity of distant events within an inertial system. For a particular closed light path, they derived a necessary condition and claimed that it could be violated by a nonstandard choice of the definition of simultaneity. It is pointed out here that (as shown by many authors) the possibility of a nonstandard definition is implicitly contained in a generally covariant formulation of the special theory of relativity, and it is shown that conditions such as the one they derived are satisfied automatically. The most general position-independent definition of simultaneity is given, and an example of a position- as well as direction-dependent definition is exhibited in an Appendix. A number of objections against the possibility of a nonstandard definition of simultaneity raised by various authors are discussed and are found to lack any physical or mathematical justification.