Special Relativity Teaches the One-Way Velocity of Light Is Measurable Without Synchronized Clocks and Clocks Are Synchronizable Without One-Way Signals

Abstract

Recent authors have addressed the Reichenbach assertions that the one-way velocity of light, OWVL, cannot be measured because we lack a method to synchronize distant clocks, and that one needs OWVL to synchronize distant clocks. Thus, one may have any OWVL provided it is greater or equal to c/2 and the round-trip velocity is c, and, since clocks can be synchronized only by light signals, clock synchronization depends on whatever OWVL happens to be. I show that the Dragowski and Wlodarczyk proposal to use transverse Doppler shifts to measure one-way velocities cannot succeed. In fact, OWVL is measurable in a synchronization-free manner by determining the minimum wavelength transmitted by an airgap optical barrier. OWVL along three non-coplanar axes is required to determine that OWVL is c. Also, contrary to the Thyssen claim that distant simultaneity is conventional, I show that, using a moving clock, relativistic time-dilation allows the synchronization of isochronized stationary clocks without knowing OWVL and also allows, separately, the measurement of OWVL. A burst of unstable particles is a suitable moving clock. Thus, one-way velocity and synchronization are shown to be independent concepts. The wavelength transmitted by an airgap and the decay of unstable particles have been neglected regarding OWVL, but all experiments in these areas have found the one-way velocity of light is c.