Precisely similar ideas are applicable to the molecules that form the air in a room.... The classical mechanics now predicts that the whole energy of motion will be changed into radiation [heat], so that the molecules will shortly be found lying at rest on the floor... In actual fact they continue to move with undiminished energy, forming a perpetual-motion machine in defiance of classical mechanics.... We have passed from one to another of three worlds... from the man-sized world to the world of the electron.

Physics and Philosophy (1942)