Clock synchronization and isotropy of the one-way speed of light

Abstract

Experimental tests of the isotropy of the speed of light using one-way propagation are analyzed using a test theory of special relativity. It is shown that, when properly expressed in terms of measurable quantities, the results of such experiments are independent of the method of global synchronization of clocks. Experiments analyzed include a Jet Propulsion Laboratory time-of-flight measurement, a resonant two-photon absorption experiment, the Smithsonian Astrophysical Observatory-NASA 1976 rocket gravitational redshift experiment, and M\"ossbauer rotor experiments. If the characteristic anisotropy is proportional to $\ensuremath{\alpha}w$, where $w$ is the velocity of the Earth relative to the cosmic background radiation, the best bound on $\ensuremath{\alpha}$ from these experiments is $|\ensuremath{\alpha}|<9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$.