SIMULTANEITY, CONVENTION AND GAUGE

Although everyone admits that in relativity theory simultaneity is frame-relative, there is still widespread resistance, after more than one hundred years, to Einstein's contention that in a given frame simultaneity, or equivalently, the one way speed of light, is conventional. Part of the resistance derives from absence of clearly articulated senses in which some feature in a physical theory is or is not conventional. I have a modest result that identifies the exact sense in which simultaneity is conventional, and thus should put closure on Einstein's long disputed conventionality thesis. But more than this, the exact sense in which simultaneity is conventional is intimately connected to the sense in which Einstein's hole argument reveals a gauge freedom in general relativity. Both can be seen as corollaries to the permutation arguments developed by Quine, Davidson, and Putnam to draw conclusions about the nature of reference. The question remains, what this has to do with gauge field theory.