News that the earth rotated on its axis and revolved around the sun was a shock. People lost the earth as an absolute reference for "up," "down," "moving," and "still." So scientists concocted the theory of "ether." The ether was the stationary, three-dimensional, intangible "grid" against which position and velocity could be measured absolutely. It was the last vestige in science of God as the unmoved mover, the Aristotelian God, the supreme absolute to which the material world is relative. By the end of the 19th century, God had disappeared from natural science as the special creator of the world and its inhabitants, and as the objective judge of morality. But the idea of an unmoving absolute against which scientific measurements could be compared survived as the "ether."
The theory of the "ether" predicted that light (traveling relative to the ether) would seem to move faster when it traveled against the direction the earth is moving (relative to the ether) and slower when it traveled in the same direction. Experiments failed to corroborate this prediction, and the ether went away.