Chapter 9 Summary and Analysis

Chapter 9 is called "Entropy and Its Demons (You Cannot Stir Things Apart)." "Entropy" was a term that was not widely understood when Shannon used it in his theory of information. The word had first been used in thermodynamics to describe the availability of energy in a system. A closed system made up of a hot part and a cold part would eventually reach an equilibrium as the heat passed from the hot part to the cold part. As the energy moved from one part to another, it had the potential to do work, but once everything became the same temperature, no work could be done. "Entropy" was first used by Rudolf Clausius in 1865 to describe this unavailability of energy.

James Clerk Maxwell suggested that the meaning of the word be reversed, to describe instead the part of energy which was available...