Arthur Eddington

Arthur Eddington led the 1919 eclipse expedition that confirmed general relativity and made Einstein famous overnight. He was a Quaker and a conscientious objector, and the expedition happened partly because his colleagues argued to the tribunal that sending him abroad on scientific work was a better use of him than prison; the idea of a British expedition to verify a German theory months after the armistice was itself the point some of them were making. Two parties went out in May 1919, one to Principe off West Africa and one to Sobral in Brazil, to photograph stars near the eclipsed sun and measure whether their apparent positions were displaced by the sun's gravity. The results favoured Einstein over Newton, and the announcement in November put relativity on the front pages. The Sobral plates from one telescope were poor and were set aside, which has been argued about ever since - the modern reanalysis supports the decision, but it was a judgement call made by the man who wanted the answer. His scientific work independent of that was substantial: he established that stars are held up by radiation pressure as well as gas pressure, derived the mass-luminosity relation, and argued that stellar energy must come from subatomic sources when no known process could supply it. He quarrelled bitterly with Chandrasekhar over whether a sufficiently massive star could collapse indefinitely, and was wrong. He wrote popular books that taught a generation what relativity was, and spent his last years on a Fundamental Theory attempting to derive the physical constants from pure reason, which no one has been able to make sense of. He was president of the Royal Astronomical Society and was knighted in 1930. Asked whether it was true that only three people understood relativity, he is said to have paused and asked who the third was. The Eddington limit on stellar luminosity carries his name.

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