ABSTRACT
This chapter introduces the thermodynamics of information, a concept that finds wide use in physics and astrophysics. The link between physics and information began in 1867, with James Clerk Maxwell's thought experiment of a creature capable of beating the second law of thermodynamics. Entropy can therefore be said to represent the missing information about a system that can't be accounted for in macroscopic descriptions; the larger the entropy, the more the missing information. When Maxwell introduced the demon, the distribution of speeds of the atoms of a gas at a fixed temperature had only recently been established. The demon dies an entropic death because it must discard information previously collected. One may reasonably assume that a measurement procedure is fundamentally associated with a certain definite average entropy production, and that this restores concordance with the second law. The physicist Leo Szilard undertook a careful examination of the role played by the involvement of an observer.
