Why is it that, in the world in which we happen to live, it is the causes which actually do precede the effects; or to put things in another way, why do precisely coordinated particle motions occur only after some large-scale change in the physical state and not before it? In order to get a better physical description of such things, I shall need to introduce the concept of entropy. In rough terms, the entropy of a system is a measure of its manifest disorder.
