Detail map of London, England, United Kingdom,Porto Real, Príncipe, São Tomé and Príncipe,Ceará, Brazil

A: London, England, United Kingdom, B: Porto Real, Príncipe, São Tomé and Príncipe, C: Ceará, Brazil

Dyson & Eddington Provide the First Experimental Proof of General Relativity

Solar eclipse as reproduced by Dyson and Eddington.
Solar eclipse reproduced by Dyson and Eddington.

Among the experimental results predicted by Albert Einstein’s 1916 theory of general relativity was the bending of light by massive bodies due to the curvature of spacetime (space-time) in their vicinity. To test this prediction, Astronomer Royal Frank Watson Dyson and astronomer Arthur Stanley Eddington organized two expeditions—one to Principe Island off West Africa, and the other to Sobral in Brazil—for the purpose of observing the solar eclipse on May 29, 1919; the sun served as the “massive body,” and an eclipse was necessary in order to observe the light coming from other stars.

“The results were in agreement with Einstein’s prediction, the Sobral result being 1.98 ± 0.12 arcsec and the Principe result 1.61 ± 0.3 arcsec [about twice the amounts predicted by Newtonian theory]. Because of the technical difficulty of these observations, the precise value of the deflection remained a controversial issue, which was not laid to rest until the development of radio interferometric techniques in the 1970s” (Twentieth Century Physics III, 1722-23).

On November 6, 1919  Dyson reported to a joint meeting of the Royal Society and the Royal Astronomical Society concerning A Determination of the Deflection of Light by the Sun’s Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919. The paper, reproducing photographs of the eclipse made by Eddington, was published in the Philosophical Transactions of the Royal Society in 1920.

In response to the paper, the president of the Royal Society, Sir J.J.Thomson, said,

“This is the most important result obtained in connection with the theory of gravitation since Newton’s day, and it is fitting that it should be announced at a meeting of the society so closely connected with him. . . . The result [is] one of the highest achievements of human thought” (quoted by Pais, Subtle is the Lord, 305). 

On November 7 confirmation of Einstein’s discovery was headlined in The Times of London, and on November 9 in The New York Times. This article was copied or adapted by newspapers all over the world, and it had the effect of turning Einstein, whose fame had previously been limited to the theoretical physics community, into a world-famous celebrity.  For the rest of his life Einstein remained the world’s most famous scientist, and relativity remained the puzzling, but fascinating subject that most people did not believe they could understand.


Timeline Themes