Today most people will have very little difficulty with the idea of motion continuing indefinitely. Since the advent of the space age we have grown accustomed to the idea that space probes can leave the solar system, traveling endlessly onward through empty space. We also are familiar with the notion that atoms, molecules, and sub atomic particles are all in a continuous state of ceaseless motion. We are comfortable with the concept of the planets, stars, and galaxies all spinning, rotating, and forever moving through empty space. A citizen of earlier centuries, if told these facts, would have immediately asked, "What is driving these bodies? What is keeping them moving?" In earlier times, all moving bodies seemed to eventually stop. Continuous motion seemed against nature. Early ideas about the movements of planets had mythical horses pulling them through the sky. The concept...