Why is it an illusion?!?! Why isn't it just a matter of perspective? Both are equally real - they just depend on where you watch from. - Regner You are mathmatically correct , I did say reference frames were a mathmatical tool, unrelated to reality. I find it strange that you consider two different perspectives as equal reality. There can only be one truth. Perspective is an illusion, unless you already agree with our proposition that the sun moves across the sky of a stationary earth! re the travelling ball: Both cannot be equally real with respect to the ball itself which I am discussing.. What is the ball in truth and reality doing? Thats real science. But perspectives could be equally illusions, to the observer on the plane or the alleged stationary observer outside the plane. Unless we could establish an absolute stationary point, (which geocentrism does) then we must assume all the different observations are illusions, appearances. i.e. relative. But in the jet plane I know the 2 ft drop in a straight line is an illusion, because with my intellect I know that I and the ball are travelling 600mph. That much I know. These are the only motions to consider for the geocentrist, but for the heliocentrist there is no end, even at galactic motion.. What is the galaxy motion referenced to.? etc etc etc... Philip.