Laplace's Demon

A Laplace's demon is the hypothetical intellect imagined by Pierre-Simon Laplace in 1814: an entity possessing complete knowledge of all forces and all positions in the universe at one moment, and endowed with sufficient computational power to calculate the entire past and future from that single snapshot. The demon is not a physical prediction but a philosophical thought experiment that makes explicit the determinism implicit in Newtonian mechanics and classical mechanics: if the universe is a mechanical system governed by differential equations, then its state at any time fixes its state at all other times. The demon is the limit case of the mechanical philosophy taken to its logical extreme — a universe without contingency, novelty, or genuine openness. The thought experiment remains influential not because the demon is possible but because it reveals what a fully deterministic universe would look like, and thereby clarifies what is lost when determinism fails.