The test that convinced the world that Albert Einstein was right about the universe was enmeshed in the history of World War I: The fighting affected which researchers failed and who succeeded, and when. When scientists finally did the key observations 100 years ago, on May 29, 1919, their feat acted as an antidote to leftover bitterness between former enemies Germany and England.

Testing the theory of relativity required precise observations of starlight during a total solar eclipse. One German astronomer chasing an eclipse in 1914 got into Russia before the war started but was soon captured and detained, his equipment confiscated.

When English scientists finally tested Einstein using that 1919 eclipse, the event generated worldwide headlines and served as a symbol of reconciliation — a demonstration of science transcending nationalism. It was a story of English astronomers helping to replace the bedrock of physics formulated by their own countryman, Isaac Newton, with a theory created by a German.

Newton formulated gravity as an invisible force between massive objects. Einstein’s replaced it with the notion that objects warped space-time and deflected the paths of other objects. Most people didn’t understand Einstein’s theory, but they appreciated it nonetheless.

Einstein himself proposed using an eclipse as a test back in 1911, well before the theory was published in 1915, said historian and physicist Daniel Kennefick, author of the book, “No Shadow of a Doubt: The 1919 Eclipse That Confirmed Einstein’s Theory of Relativity.”

In Newton’s theory, starlight would be unaffected by the gravitational pull of a massive object such as the sun. In Einstein’s theory, the sun’s mass would bend space, and the starlight moving through it, creating a tiny discrepancy between the apparent positions of stars whose light passed by the sun, and those same stars at night. And as astronomers knew, the one time it was possible to observe starlight passing by the sun was during a total eclipse.

The 1914 attempt led to the arrest of the German astronomer Erwin Finlay-Freundlich. As Kennefic describes it, “The Russians rounded up all Germans as enemy aliens (which was standard practice then at the outset of war in many countries).” There might have also been suspicion that Finlay-Freundlich and his two colleagues were using their telescopes for spying. The astronomers were freed a couple of months later in a prisoner exchange. Another opportunity in 1918 failed because the American astronomers who were well-positioned to see the eclipse never got their equipment back from Russia, where they had also gone in 1914.

There was another suitable eclipse in 1916, but by then war was all over Europe. By the time of the 1919 eclipse, the war was finally over, but this was a tough one to observe, said Kennefick. The path went mostly over ocean, and where it did cross land it was over some of the most impenetrable parts of the Amazon in South America and the Congo Basin in Africa. And by that point, the Germans were not in a position to fund any expeditions.

But word of Einstein’s theory had reached English astronomer Arthur Eddington. He and some colleagues went to Principe Island off the west coast of Africa, and as a backup, another English astronomer, Frank Dyson, organized an expedition to the town of Sobral, Brazil. Both groups got a mix of failed images and good ones, and the good ones looked to confirm Einstein by showing the starlight deflected by the predicted amount.

Kennefick said the news caught the public imagination in a big way, and Einstein became an overnight celebrity. According to a story in Discover magazine, the front page of The London Times ran the headline “New Theory of the Universe: Newtonian Ideas Overthrown.” The New York Times reported: “Men of Science More or Less Agog.”

The feat helped dissolve bitterness left by the war, said Kennefick. But history moves on. One of the consequences of Einstein’s re-imagining of the universe was the equation E=mc2, which made people realize that a weapon like no other might be possible. And that changed everything.

Historians still argue whether scientific advances really represent progress, either in the human condition or our collective wisdom. But advances in science and technology prevent history from repeating itself, at least not exactly. The cycles of peace and war continue as always, but the nature of both continues to change each time around.

Science writer Faye Flam is a Bloomberg Opinion columnist. She has written for The Economist, The New York Times, The Washington Post, Psychology Today, Science and other publications. She has a degree in geophysics from the California Institute of Technology.

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