ABSTRACT
When the great nineteenth-century physicist James Clerk Maxwell imagined (1871, 308) “a being whose faculties are so sharpened that he can follow every molecule in its course,” he could not have foreseen the unlikely career his thought creation would have. A little over 50 years later, in a thought experiment devised by Leo Szilard and published in 1929, the demon was manipulating a single molecule and providing the grounding for a connection between information gathering or information processing and thermodynamic entropy. That 1929 thought experiment and its subsequent reception will be the principal subject of this chapter.
