Not Only Because of Theory: Dyson, Eddington, and the Competing Myths of the 1919 Eclipse Expedition

One of the most celebrated physics experiments of the twentieth century, a century of many great breakthroughs in physics, took place on May 29th, 1919, in two remote equatorial locations. One was the town of Sobral in northern Brazil, the other the island of Principe off the west coast of Africa. The experiment in question concerned the problem of whether light rays are deflected by gravitational forces, and took the form of astrometric observations of the positions of stars near the Sun during a total solar eclipse. The expedition to observe the eclipse proved to be one of those infrequent, but recurring, moments when astronomical observations have overthrown the foundations of physics. In this case it helped replace Newton’s Law of Gravity with Einstein’s theory of General Relativity as the generally accepted fundamental theory of gravity. It also became, almost immediately, one of those uncommon occasions when a scientific endeavor captures and holds the attention of the public throughout the world.