Can science exist apart from politics? On May 29, 1919, British astronomer Arthur Eddington was doing his best to find out. Eddington had been preparing for this day throughout much of the Great War, trying to keep the prejudices of the moment separate from the pursuit of knowledge. Less than a year earlier, Eddington had finalized plans to test of a new theory of gravity proposed by a German-born scientist, even as the German army was shelling Paris and waging one of the bloodiest campaigns of World War I.

That scientist was Albert Einstein, not yet famous enough to serve as Eddington’s get-out-of-jail-free card—and staying out of jail was exactly what Eddington had been trying to do.

In 1918, the British military, desperate to replenish its ranks after more than three years of fighting, started reviewing all cases for which it had granted exemptions from the draft. Eddington’s exemption was based solely on his research as director of the Cambridge University Observatory, but on June 14, a military tribunal told him that the reason was no longer sufficient. A lifelong Quaker, Eddington tried pleading his case as a conscientious objector. The court refused to consider that argument, calling the case “a very hard one—hard against Prof. Eddington,” but gave him a deadline of July 11 to convince them otherwise.

Eddington had never been shy about expressing his Quaker beliefs, even while living and working on a Cambridge campus where five undergraduates and fifteen graduate students had been arrested for refusing military service. At a time when a Cambridge professor proclaimed that “the Germans are congenitally unfit to read our poetry; the very structure of their organs forbids it,” and the prestigious British journal Nature published articles decrying the inferiority of German science, Eddington publicly urged British astronomers to keep the wartime horrors separate from their work.

In particular, he championed Einstein’s radical new work on gravity. If Einstein’s theory was correct, it would replace Isaac Newton’s view of gravity as a force that acts across space with the revolutionary idea that gravity is space. Einstein asserted that space and time, instead of being stiff and unchanging, can buckle or sag due to the presence of a massive body, much the way a heavyweight sleeper sags a mattress. A marble rolls toward a heavy body not because of a force but because the body has dimpled the space-time through which the marble must travel.

As counterintuitive as Einstein’s theory seemed, Eddington knew there was a way to test the theory. Einstein himself had suggested the method.

If a body is massive enough—like the Sun—then it should be possible to observe the curved or bent path of all objects traveling in its vicinity, even particles of starlight. The bending of starlight would show up as a change in the apparent position of the star compared to its position when the Sun was in another part of the sky.  Under ordinary conditions, the blinding light of the solar disk would completely swamp the much fainter light from surrounding stars. But during those rare times and places when the clockwork motion of the solar system places the Moon directly between the Sun and Earth—a total solar eclipse--the stars pop into view.

When the military tribunal reconvened on July 11, 1918, to decide his fate, Eddington presented a letter from Frank Dyson, Britain’s Astronomer Royal and chair of the Joint Permanent Eclipse Committee of the Royal Society and the Royal Astronomical Society. The carefully crafted note highlighted the pursuit of science but also played on the emotions of wartime Britain. Dyson asserted that the total eclipse of the sun in May 1919, visible across Africa and Brazil, was of exceptional importance and that Eddington was the best person to lead a British expedition to observe it—an experiment, Dyson added, that would counteract “a widely spread but erroneous notion that the most important scientific researches are carried out in Germany.”

The letter did the trick. The local tribunal said it was convinced that Eddington was a true conscientious objector and that his work was of vast importance “not only to this country but to the world—to knowledge generally.” And so it was that during some of the fiercest fighting of the war, Eddington got the official go-ahead to test Einstein’s theory.

The 1919 event had several things going for it. The eclipse would last more than six minutes, one of the longest in the twentieth century. What’s more, the sun would be sitting against a rich background of stars, the Hyades cluster, providing a bounty of objects with which to test Einstein’s light-bending prediction. Another plus: these stars were relatively bright.

By the time Eddington and his colleagues set sail to observe the eclipse, the war was over. Eddington and a collaborator journeyed to Principe, a Portuguese-owned island off the west coast of Africa, while a second British team traveled to Sobral, in northern Brazil. At Principe, clouds nearly obscured the observations. At Sobral, the lens of the main telescope had become distorted, apparently due to the sun’s heat, producing photographic plates that were out of focus.

Yet when Eddington and his colleagues went back to England and compared the positions of the stars they were able to image during the eclipse with the positions when the sun was elsewhere in the sky, they found the amount of light bending that Einstein had predicted (more recent assertions that Eddington had fudged the data in favor of Einstein have been shown to be incorrect).

The day after Eddington announced the results at a meeting of Royal Society in London on November 6, 1919, the front page of the Times of London was full of stories about war and remembrance. It was only a few days before the first anniversary of the armistice, and King George V had just issued an invitation for all workers to take two minutes of silence out of their day to remember and honor “the glorious dead.” But to the right of these stories appeared an article about rebirth and renaissance. In a triple-decker headline, the normally staid Times wrote: “Revolution in Science / New Theory of the Universe / Newtonian Ideas Overthrown.”

The news set off a chain reaction around the globe. The New York Times followed suit with a front-page story on November 10: “Lights All Askew in the Heavens . . . Einstein Theory Triumphs.”

A century later, Einstein’s theory of gravitation continues to open new and unexpected windows on the birth and life of the cosmos. The discovery of gravitational waves—invisible undulations in space-time that provide a new way of learning about exploding stars and some of the most violent collisions in the universe—and the existence of black holes and their shadows, one of which was recently imaged for the first time--were both predicted by Einstein’s theory.

International collaborations are now commonplace and an expedition like Eddington’s would almost certainly include scientists from a multitude of countries. But in today’s polarized climate, the question may be important than ever: Can science remain separate from politics?

All scientists can do is keep on trying.

This essay is adapted from the author’s new book Gravity's Century: From Einstein's Eclipse to Images of Black Holes, published by Harvard University Press.