Jack L Therefore why aren't Michaelson and Morely et al scientific heroes? I'm on very shaky ground here, but my understanding is that the experiment to which you are probably refering was interpreted by the two 'camps' to have had different conclusions. Had the non revolving Earth conclusion been correct, then the way the universe works would have been very different from the way it is understood to work. [Robert Bennett] The difference in understanding between GC and HC/AC would be very great. However the difference in observations would be very slight - the difference between aether and gravity has only been detectable for about a century. But more GC proofs are unfolding each day. In this position, I'd venture the guess that none of the space missions outside the Earth/Moon system would have succeeded, instead of which a quite large proportion have succeeded hansomly. [Robert Bennett] The old canard - that you must use HC to navigate in the Solar System - is contrary to general covariance and exposed in GWW as a myth promoted by a certain USA space agency. Does ESA insist that they use HC navigation - because they must? On shaky ground... yes then why venture the guess? RB Paul D