The turmoil and disruptions of World War I, for example, prevented many people from learning and thinking about general relativity. The theory’s earliest converts included a Russian mathematician being held in a German prisoner-of-war camp, who was unable to enlighten his Russian colleagues for several years; a German astronomer being held in a Russian prisoner-of-war camp, who was unable to complete his test of one of the theory’s key predictions; and another German astronomer, who passed the time while serving in the German Army by finding the first exact solutions to Einstein’s equations, only to succumb to a deadly disease on the Russian front a few weeks later.

The war also controlled how Einstein’s work spread westward. Because he was a German civil servant, neither Einstein nor his letters — nor even German scientific journals — could cross the English Channel amid the naval blockade. Einstein could, however, travel to neutral countries, like the Netherlands. He made frequent trips to Leiden, where he befriended the great mathematical physicist Willem de Sitter and tutored him in general relativity. And de Sitter, in turn, sent a series of detailed primers on Einstein’s work to a Cambridge colleague, the physicist and astronomer Arthur Eddington.

Eddington, a Quaker and conscientious objector, was concerned that wartime resentments were damaging the international scientific community. He leapt on Einstein’s relativity as a means of restoring harmony. As the historian Matthew Stanley has documented, Eddington’s superiors in London and Cambridge lobbied British government officials to let him devote his mandatory wartime service to preparing an astronomical expedition to test one of Einstein’s major predictions, that gravity could bend the path of starlight. By leading a British team to test the work of a German physicist, Eddington hoped to “heal the wounds of war.”