Just what is this entropy stuff, anyway? The atomic hypothesis provides an answer. Heat is a form of energy, and entropy is associated with heat. If things are made out of atoms, then there is a simple explanation of heat: heat is just the energy in the jiggling of atoms. Entropy, then, has a simple interpretation, too: To describe the motion of atoms requires a large number of bits of information. The quantity called entropy is proportional to the number of bits required to describe the way atoms are jiggling.
