Albert Einstein had a genius for extracting revolutionary theory from simple considerations: From the postulate of a universal velocity he created special relativity; from the equivalence principle he created general relativity; from elementary arguments based on statistics he discovered energy quanta. His 1905 paper on quantization of the radiation field (often referred to, inaccurately, as the photoelectric-effect paper) was built on simple statistical arguments, and in subsequent years he returned repeatedly to questions centered on statistics and thermal fluctuations. In 1909, Einstein showed that statistical fluctuations in thermal radiation fields display both particlelike and wavelike behavior; his was the first demonstration of what would later become the principle of complementarity. In 1916, when he turned to the interplay of matter and radiation to create a quantum theory of radiation, he once again based his arguments on statistics and fluctuations.
Einstein’s theory of radiation is a treasure trove of physics, for...
