- Einstein's Jury: The Race to Test Relativity
Many popular-science books offer a clean story of how general relativity began: Einstein single-handedly developed it to extend his special relativity of 1905. The theory interpreted gravity as an effect of mass distorting space-time, and provided three empirical predictions: Mercury's perihelion movement, the deflection of starlight by the Sun, and the red shifts of the solar spectra. The first prediction explained some long-standing irregularities, while the second was confirmed by Arthur Eddington's famous eclipse observation in 1919. These verifications marked the triumph of general relativity.
Decades of historical studies have problematized this origin myth. But Jeffrey Crelinsten's new book goes further. Above all, he displaces Einstein from the centre of the stage. Not even those mathematicians and physicists whom we usually associate with relativity appear on the top of the cast. Instead, Crelinsten's main characters are astronomers with lesser visibility: William Campbell, Herber Curtis, John Evershed, Erwin Freundlich, Charles St John, etc. Most of them came not from the contemporary epicentres of physics in Europe, but from observatories – Mt Wilson and Lick – in the scientifically less-advanced United States. Their drama consisted of calibrations of photographical plates and analysis of spectroscopic data, not Riemannian geometry and tensor equations. By focusing on these figures, Crelinsten charts an important but understudied episode in the history of modern physics: the empirical tests of general relativity.
Under Crelinsten's inspection, the process of testing general relativity was much more complicated than the popular-science account. None of Einstein's three predictions received an unambiguous confirmation in a test or two. Take the deflection of starlight, for example. Although Eddington supported the relativistic prediction with his 1919 eclipse expedition, many astronomers were skeptical of his conclusion. In fact, Lick Observatory voted against Einstein on the basis of its own eclipse data in 1919. Not until the Lick staff collected data from more eclipse expeditions in 1920–25 did they fully support the relativistic prediction. It was the accumulation of these endeavours, not a single critical test, that convinced the astronomy community of the relativistic prediction. Similarly, Einstein's theory of mercurian precession was not an effective explanation for many astronomers in the 1910s. At the time, some stardust theory offered an account for the same phenomenon. It took astronomers years of efforts to expose this theory's problems before accepting the relativistic explanation. If there is a lesson from Crelinsten's story, it is the improbability of the single 'crucial experiment.' The empirical testing of a theory is a long process with multiple fronts. [End Page 331] The temporary failure or success at one front does not often dictate the next direction of development, let alone the theory's eventual destiny.
Crelinsten devises a narrative structure consistent with such themes. In part 1 of Einstein's Jury, he introduces Einstein's early work on relativity and sets the stage for the astronomy community in the 1900s. Here Crelinsten situates the rise of American astronomy in the context of the US expansion of investment on scientific research in the early twentieth century. Part 2 concerns Einstein's three empirical predictions and astronomers' unsuccessful attempts to verify the predictions circa the First World War. Part 3 describes the full-fledged astronomical tests of general relativity in 1920–25. During this period, American astronomers made many solar spectra and eclipse measurements. Their data eventually led to the acceptance of general relativity in 1925–30 among the astronomy community, as depicted in part 4.
Crelinsten is a believer in details. He diligently documents exchanges of ideas, conducts of experiments, and steps of arguments. He utilizes two kinds of sources. Regarding Einstein and other European physicists, Crelinsten relies on published documents and the secondary literatures. To delineate American astronomers' activities, he uses a lot of unpublished archival substances.
If there is anything to improve in this book, it is the way of presenting materials. Crelinsten provides a thematic introduction and an analytical conclusion, which seem to be the only places at...