Einstein Synchronisation and the Conventionality of Simultaneity

Despite a broad-range title the paper settles for the related issue of whether the Special Theory of Relativity (STR) necessarily advocates the demise of an ontological difference between past and future events, between past and future in general. In the jargon of H. Stein: are we forced, within the framework of the STR, to choose only between ‘solipsism’ and ‘determinism’ exclusively? A special emphasis is placed on the role that the conventionality of simultaneity plays in the STR with regards to this question. The standard arguments rely on the relativity of simultaneity, the claim that the STR negates the existence of a universal ‘present’ that divides the ‘past’ and the ‘future’, so as to conclude that there is no ontological difference between past and future events, that both are equally determined/real (‘determinism’). This often neglects the fact that to establish the ontological claims related to relativity of simultaneity, one must first resolve the issues of conventionality of simultaneity within the STR. The paper will aim to show that by addressing the issue of conventionality from Dummett’s ‘purely philosophical’ determination of the difference between the past and the future, we develop an understanding of the said difference, within the framework of the STR, beyond the (unwanted) strict ontological dichotomy of ‘solipsism/determinism’, given that the criterion that is provided by the STR is understood as epistemic and not ontological.