I'm confused by something I read, that said: Ref: http://adsabs.harvard.edu/abs/1988AmJPh..56..811B What does that last statement (underlined by me) mean, "any anisotropy in the speed of light is contrived and not physically significant". Why is it not physically significant? I thought the very definition of isotropy confirmed physical significance. Seems like it should be physically significant in both experimental verification and application of the Einstein convention. And how is it that it is considered contrived? I mean I know we pick a convention, but that doesn't mean it's contrived, or does it?