ABSTRACT
Pierre-Simon Laplace's demon is a disembodied intelligence with access to infinitely detailed information about the states of all particles in the universe: an idealized observer with perfect knowledge of the initial conditions from which any future or past state could be calculated in a completely deterministic world. In nineteenth-century physics, the ideal of perfect knowledge was personified rather by the "demons" of Laplace and James Clerk Maxwell. While "demons" were initially conceived to represent the ideal of perfect knowledge apart from physical factors and consequences, the possibility of cheating the second law can be conceived in strictly mechanical terms, bypassing "intelligence" per se. However, Maxwell was suspicious of attempts to prove the second law using statistical mechanics and devised a thought experiment to explore the issue. Unlike any real observer, Maxwell's demon is a disembodied intelligence, whose physical properties are negligible.
