Trust in expert testimony: Eddington's 1919 eclipse expedition and the British response to general relativity

The 1919 British astronomical expedition led by Arthur Stanley Eddington to observe the deflection of starlight by the sun, as predicted by Einstein's relativistic theory of gravitation, is a fascinating example of the importance of expert testimony in the social transmission of scientific knowledge. While Popper lauded the expedition as science at its best, accounts by Earman and Glymour, Collins and Pinch, and Waller are more critical of Eddington's work. Here I revisit the eclipse expedition to dispute the characterization of the British response to general relativity as the blind acceptance of a partisan's pro-relativity claims by colleagues incapable of criticism. Many factors served to make Eddington the trusted British expert on relativity in 1919, and his experimental results rested on debatable choices of data analysis, choices criticized widely since but apparently not widely by his British contemporaries. By attending to how and to whom Eddington presented his testimony and how and by whom this testimony was received, I suggest, we may recognize as evidentially significant corroborating testimony from those who were expert not in relativity but in observational astronomy. We are reminded that even extraordinary expert testimony is neither offered nor accepted entirely in an epistemic vacuum.