EINSTEIN'S JURY. The race to test relativity. By Jeffrey Crelinsten. 428pp.
Princeton University Press. $35; distributed in the UK by Wiley. Pounds 22.95.
0 691 12301 1
In 1915, the world glimpsed both the terror and the beauty of science. At the beginning of that year, the chemist Fritz Haber unleashed the first scientific weapon of mass destruction -poison gas -on French troops at Ypres. But in November 1915, another German scientist announced a revolution in our understanding of the physical universe. Albert Einstein's general theory of relativity was, said the physicist Max Born, "a great work of art". The quest to extend relativity to include gravity had taken Einstein more than seven years.
With characteristic honesty, he admitted the experience had been "hell". In this new theory, gravity was redefined as (in the physicist John Wheeler's words) "a manifestation of the geometry of space right where the mass is".
Einstein claimed it was not a Newtonian force of attraction that held the planets in their orbits, but the warping of the very fabric of space by massive bodies such as the Sun. As well as explaining the anomalous orbit of Mercury which had long puzzled astronomers, Einstein's revolutionary theory predicted that spectral lines emitted by large gravitating bodies would shift towards the red and that the path of light would bend as it passed through a gravitational field, tracing the warped geometry of space. As early as 1911, Einstein had challenged astronomers to test his nascent theory. In particular, he suggested a solar eclipse would provide an ideal opportunity to see if, as his theory predicted, stars "appear to be displaced outwards from the sun, as compared with their apparent position in the sky when the sun is situated at another part of the heavens".
In this impressively detailed yet readable scholarly work, Jeffrey Crelinsten examines the history of early attempts by astronomers to put Einstein's theory to the test, both in Europe and America. He charts the gradual (even grudging) acceptance of relativity and its eventual adoption (to quote James Jeans) as "one of the ordinary working tools of astronomy". Crelinsten also shows how the "astronomical center" moved from Europe to the United States, a process that began well before the rise of fascism prompted an exodus of scientific talent from the Old World. According to Crelinsten, astronomers had a "unique stake" in whether or not relativity was accepted: "astronomers make a living studying the solar system, stars, and nebulae and the overall structure of our universe.
Einstein's theory touched upon their area of expertise and promised to change it radically". Some opposed it, seeing relativity as a threat to their reputations; but others overcame their initial scepticism through vigorous testing, and they eventually embraced Einstein's paradigm-shifting idea. As well as casting new light on a neglected aspect of relativity studies, Einstein's Jury provides a fascinating analysis of science in action: the scrupulous weighing of evidence to assay as far as is humanly possible -the truth of the matter.
The dramatic announcement at the end of 1919 that the British astronomer Arthur Eddington's solar eclipse observations had verified the theory of general relativity made Einstein headline news around the world. But, as Crelinsten shows, the adoption of a scientific theory is always a "messy process".
Eddington's results were neither the first nor the last word on relativity; away from the media spotlight, the testing continued for another decade. Unlike Eddington or Erwin Freundlich in Berlin, both ardent believers in relativity, American astronomers were not motivated by a desire to verify Einstein's theory: "for the astronomers conducting the research, it was actually about precise measurement of astronomical phenomena". Indeed, as Crelinsten amusingly points out, most American astronomers did not even understand Einstein's relativity. The distinguished astrophysicist George Ellery Hale confessed to the Astronomer Royal, Frank Dyson, that "the complications of the theory of relativity are altogether too much for my comprehension". Similarly, Henry Norris Russell, "American astronomy's greatest theoretician", admitted to being "horrified" by the suggestion that he write a popular account of the theory.
Crelinsten concludes that "the empirically oriented United States" eventually accepted the theory in the late 1920s "because it had passed crucial tests, despite a lack of theoretical understanding".
According to Crelinsten, "it took roughly two decades for Einstein's jury of astronomers to pass judgment on his theory of relativity". Their verdict was based principally on evidence from eclipse photography, as well as solar and spectral spectroscopy. As a result, astronomers were transformed from being Einstein's jury into "witnesses on his behalf". American astronomers like William Wallace Campbell -described by the press as the "dean of western astronomers" -worked long and hard assembling empirical evidence on relativity.
Once convinced, they took up the cudgels on Einstein's behalf against his critics -"diehard ether enthusiasts", like T. J. See, who described Einstein's theory to the media as a "piece of Humbuggery", and Charles Lane Poor of Columbia University, who memorably labelled Einstein the "Bolshevist of Science". But such rhetoric didn't sway empirically minded astronomers like Campbell. He summed up his philosophy of science in a few apt words from Alexander Pope: "Whatever is, is right".
