The SR Question of the Century ================================= ================================= Why has no one simply used two clocks on a table to measure light's one-way speed? ================================= ================================= (Note: No, Roemer did not do it; he used slow clock transfer, where one clock spanned the Earth's orbit, and since moving clocks run slow, his clocks were asynchronous.) For those who may need it, here is a detailed version of my question: ================================= Given two new atomic clocks still in their shipping crates, how would anyone use these clocks to measure light's one-way speed in a way that is proved to be correct? ================================= Basically, I am speaking simply of the one-way version of the Michelson-Morley experiment. And if you happen to believe that the MMx round-trip experiment somehow even _implied_ one-way invariance, then you need to prove this via the critical case of a frame that moves wrt the light source. The given question is extremely important because an incorrect measurement of light's one-way speed means incorrect measurements of all one-way speeds and all time spans involving two or more clocks. The given question is also extremely important because special relativity (our current theory of time measurement) is based solely upon Einstein's light postulate, which claims light speed invariance in the one-way case.