Charles C. Mann Quote

Only in 1905 was the panels’ puzzling behavior explained—by Albert Einstein, a newly minted Ph.D. with a day job in the Swiss patent office. In what may have been the greatest intellectual sprint for any physicist in history, Einstein completed four major articles in the spring of that year. One described a new way to measure the size of molecules, a second gave a new explanation for the movement of small particles in liquids, and a third introduced special relativity, which revamped science’s understanding of space and time. The fourth explained the photoelectric effect. Physicists had always described light as a kind of wave. In his photoelectric paper, Einstein posited that light could also be viewed as a packet or particle—a photon, to use today’s term. Waves spread their energy across a region; particles, like bullets, concentrate it at a point. The photoelectric effect occurred when these particles of light slammed into atoms and knocked free some of their electrons. In Fritts’s panels, photons from sunlight ejected electrons from the thin layer of selenium into the copper. The copper acted like a wire and transmitted the stream of electrons: an electric current.