Chapter 13 Summary and Analysis

Chapter 13 is called "Information Is Physical (It from Bit)." The main title is in reference to a work by Rolf Landauer in which he examined the formula by John von Neumann that described the energy cost of information processing. Von Neumann had theorized that every operation on a bit cost energy. Landauer proved this was incorrect. Flipping a bit from one state to another did not change the entropy, and so had no cost in energy, Landauer showed. Charles Bennet, based on Landauer's theory, showed it was only when information was erased that entropy was changed and heat was dissipated.

This connection of information with entropy and the physical realm proved to have applications in quantum physics. Charles Bennet went on to design a method for passing information using qubits, or quantum bits. A problem in quantum mechanics is that the...