Well, there have been many experiments with the earth and sun. It has been proven that the earth tracts to the actual location of the sun, or about 2 degrees ahead of the apparent location that we see as the sun. I remember reading on some website a few years ago that if there were any significant lag in the planetary reaction, that the planets would spiral out of their locations. Think about it! Have some ball orbit a center point and then move the force acting on the ball so that it is pointing a few degrees off the center point. what happens to the path of the ball?