You might be correct to a certain degree, but we have to consider that the old theories to explain the motions of the planets were based on a false assumption - that the universe was geocentric. There was no way to prove otherwise at the time.<br /><br />But Einsteins theory is based on the assumption that the speed of light is constant, whatever the peculiar motion of the observer. There are many existing ways to prove otherwise, but however we test, it seems to be true.<br /><br />In 1964, scientists at CERN, a particle accelerator located on the Swiss-French border near Geneva, managed to create tiny subatomic particles called neutral pions and have them move at the speed of 0.99975c. These particles then emitted light in the form of gamma rays. Intuitively, we might think that the scientists in the lab would have measured the gamma rays speed to be 0.99975c + c = 1.99975c (i.e. the speed of the source plus c). But, observing it to within an accuracy of 0.1%, they found that it was c.<br /><br />Throughout the universe, many stars can be found in pairs known as binary star systems. Within each such system, the two stars orbit each other about their common centre of mass, moving in elliptical patterns.<br /><br />Imagine a binary system in which the planes of both orbits appear flat to us on earth so that the stars only ever have horizontal velocities as far as we’re concerned. Some of the time, each star will be moving towards us and some of the time it will be moving away.<br /><br />Given this scenario, if the speed of light varied as we might naively expect, then the speed of light from a star moving directly towards us (star A) at speed v would be c+v and the speed of it from one moving away at the same speed (star B) c-v.<br /><br />This would mean that if both stars emitted some light at the same time (and they were the same distance away from us, as in the picture above), that we would see the light from star A sooner than that from star B.<br /><br />It would also im <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>