Beyond Conventionalism: Testing the One-Way Speed of Light via Classical Entanglement Synchronization

The conventionalist thesis holds that all internal clock synchronization procedures are equivalent to Einstein’s, that the one-way speed of light is conventional (i.e., not measurable), and that the Lorentz transformations (LT) and Lorentz transformations with absolute simultaneity (LTA) are empirically equivalent. In this paper, we challenge these claims by presenting a rotating rod synchronization procedure that operates independently of light signals or information transport. This procedure is a priori not equivalent to Einstein synchronization and can be used to experimentally discriminate between LT and LTA by measuring the one-way speed of light. We analyze Sagnac-type optical effects—including the linear Wang-Sagnac effect and its reciprocal variant—showing that only the LTA preserve spacetime continuity along closed non-simply connected contours. We further examine Faraday induction from moving electrified bodies and equilibrium paradoxes in relativistic electromagnetism, showing that the LTA resolve these paradoxes. The implications for quantum entanglement synchronization and variable speed of light (VSL) cosmology are briefly explored. Our analysis indicates that the claimed LT-LTA equivalence is not general, and that experimental tests of the one-way speed of light are feasible, potentially favoring the LTA framework. In particular, we find that the reciprocal linear Sagnac effect preserves reciprocity—a hallmark of the relativity principle—under the LTA, whereas the LT fail to do so, indicating that the LTA offer a more consistent description of relativistic phenomena across a wider class of physical scenarios.