Aristotle's Physics is about the causes of motion and culminates in a proof that God is needed as the ultimate cause of motion. Aristotle argues that things in motion need to be moved by something other than themselves - he rejects Plato's self-movers. On pain of regress, there must be an unmoved mover. If this unmoved mover is to cause motion eternally, it needs infinite power. It cannot, then, be a body, since bodies, being of finite size,...