The Eclipse That Made Einstein Famous Two Tomes Revisit the 1919 Solar Eclipse That Confirmed a Key Prediction of Relativity Theory

INSIGHTS

RELATIVITY The eclipse that made Einstein famous Two tomes revisit the 1919 solar eclipse that confirmed a key prediction of relativity theory

By Andrew Robinson which light could not be deflected by gravity. of the photographs taken on that expedition “Relativity’s sudden explosion, and Edding- showed the errors were as great as the effect n 6 November 1919, British astrono- ton’s zealous evangelism for it, would never they were trying to measure.” Although the mers—led by Arthur Eddington, the have happened in quieter times,” Stanley evidence inherent in the photographic plates Plumian Professor of Astronomy at argues. “If Eddington had not cared about is complicated, it seems to acquit Eddington the University of Cambridge, and pacifism, we would not have had the relativ- of fudging the data, if not of having a theo- Frank Dyson, the Astronomer Royal— ity revolution in 1919.” retical bias in favor of Einstein’s theory. announced that their observations of By contrast, Kennefick writes, “I find it According to Kennefick, one aspect of Oa solar eclipse on 29 May from Principe, an difficult to believe that Eddington’s experi- the eclipse expeditions has long been un- island off the coast of west Africa, and Sobral, ence of being a pacifist during derestimated. Dyson’s role, he a city in northeastern Brazil, had confirmed the war led him to expect public argues, was just as important a key prediction of Albert Einstein’s contro- approbation for his efforts.” The as Eddington’s.

versial theory of relativity. Suddenly, Einstein vital ingredient in Eddington’s Dyson was a long-time skeptic Downloaded from became famous on both sides of the Atlantic. success, he argues, was his scien- of relativity. Indeed, it was not un- When he visited the United States in 1921, tific background: “He was a theo- til 1922, after another set of eclipse New Yorkers lined the streets to cheer his ar- rist with the right mathematical observations, that he declared, “I rival. But when he then traveled to London training.... In addition, he had don’t think there is ‘any possible and gave a lecture at King’s College, the over- done extensive work in astrome- shadow of doubt’ about the cor- Einstein’s War

flowing audience kept silent when Einstein try, the skill required for actually rectness of Einstein’s prediction http://science.sciencemag.org/ Matthew Stanley mounted the platform. Only after he had won carrying out the observational Dutton, 2019. 400 pp. of the deflection of light, whatever them over came a storm of applause. test.” “It is true that Eddington difficulties may be found with the Why such a disparity? The answer lies in and Einstein shared pacifist ide- rest of his theory.” His change of the lingering anti-German sentiments in als and internationalist senti- mind speaks of the convincing Britain in the wake of World War I. Despite ment,” Kennefick continues, “but quality of the data collected from the fact that unlike many of his colleagues, their common scientific interests the 1919 expeditions. Einstein did not contribute to any military are what brought them together.” Even more important, Dyson projects, he had nonetheless published his Both books deal with allega- alone was clearly the one who car- theory in Germany at the height of the war. tions against the expedition ried out the analysis of the Sobral Relativity’s relationship with the world war astronomers—Eddington in par- data that confirmed Einstein’s

and the story of the eclipse that confirmed a ticular—that their results were No Shadow of a Doubt prediction. The data from Prin- on May 9, 2019 Daniel Kenneﬁ ck key component of Einstein’s theory are the not as conclusive as they claimed. cipe obtained by Eddington, Ken- Princeton University subject of two remarkable books published In short, Eddington claimed more Press, 2019. 413 pp. nefick asserts, were too meager for the centenary of the latter’s observations. precision for the observations for definite conclusions because No Shadow of a Doubt by physicist and Ein- than was technically possible in 1919. “This cloudy weather obscured the sun. stein scholar Daniel Kennefick is intended proof of a German theory by British scientists Given how severely limited the available more for academics than for general readers, was hailed as a great act of reconciliation be- data were in 1915, how did Einstein come up with far more technical detail on the eclipse tween the two countries after the war,” wrote with his theory? He developed it from a very observations than Einstein’s War by historian Stephen Hawking in A Brief History of Time. narrow empirical base, relying primarily on of science and Eddington scholar Matthew “It is ironic, therefore, that later examination his scientific imagination, notes Kennefick. Stanley. His book skillfully interweaves the But it has passed every subsequent test for lives of Einstein and Eddington into a read- more than a century, most recently its predic- able narrative. tion of gravitational waves and black holes. Kennefick and Stanley cover similar mate- When Einstein lectured on “The origin of rial, and their interpretations of the eclipse the general theory of relativity” at the Uni- observations are broadly comparable. How- versity of Glasgow in 1933, he disarmingly ever, they differ substantially in their inter- confessed, “In the light of the knowledge pretation of the influence of World War I on attained, the happy achievement seems the reception of the observations. almost a matter of course, and any intelli- In Stanley’s view, Einstein had to fight a gent student can grasp it without too much private “war” with skeptics who believed in trouble. But the years of anxious searching Isaac Newton’s absolute space and time and in the dark, with their intense longing, their the long-established concept of “ether,” in alternations of confidence and exhaustion and the final emergence into the light—only those who have experienced it can under- The reviewer is a freelance writer and the author of Einstein: j A Hundred Years of Relativity (Princeton Univ. Press, 2015). Eddington’s (right) 1919 eclipse observation stand that.”

PHOTO: ROYAL ASTRONOMICAL SOCIETY/SCIENCE SOURCE SOCIETY/SCIENCE ASTRONOMICAL ROYAL PHOTO: Email: [email protected] confirmed Einstein’s (left) theory of relativity. 10.1126/science.aax1447

SCIENCE sciencemag.org 10 MAY 2019 • VOL 364 ISSUE 6440 537

Published by AAAS The eclipse that made Einstein famous Andrew Robinson

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