This is the very readable and fascinating story of two scientists, the British astronomer Arthur Eddington and the German physicist Albert Einstein, who were brought together during the Great War via the vehicle of General Relativity. The German destruction of the Belgian city of Louvain, including its famous university and library, at the start of the war set in motion a chain of events that cut both Einstein and Eddington off from their intellectual communities. Profound and deep hostility developed between British and German scientists as international relations crumbled. While in Germany scientists accused the English of not giving Germans enough credit, the British, in turn, decided that the Germans were not that good at science. Scientific institutions purged members from enemy nations. In this context, the two scientists stood out: Einstein was a pacifist and internationalist while most of the rest of German society and scientists embraced an uncritical nationalism; Eddington was a pacifist Quaker who refused military service in an increasingly chauvinistic Britain.

Matthew Stanley describes Einstein's early scientific career and biography, including a complicated private life, which led to a comfortable scientific position in Berlin on the eve of war. Einstein's determined pursuit of General Relativity during the war, despite life-threatening malnutrition and disease caused by shortages on the German home front as well as occasional chaos in his personal life, culminated in a race he won, competing with the mathematician David Hilbert to find the right equations. The physicist's scientific brilliance was accompanied by a sometimes naive political conduct. Einstein signed internationalist manifestos, published essays critical of the war, and thereby drew the attention of German wartime censors.

Einstein's War also surveys Eddington's life and career, which were marked by his scientific excellence, including the mathematical ability necessary to understand General Relativity, but also by the consequences of being a Quaker who rejected war. As the First World War dragged on and casualties mounted, conscientious objectors were treated very harshly in Britain, as if they were traitors to the national cause. When a fellow astronomer called for the exclusion of Germans from the international scientific community, Eddington replied by publishing some conciliatory remarks about German scientists, defending internationalism in science and trying to humanize the enemy. A senior colleague responded by pointedly reminding the astronomer that conscientious objectors like Eddington should not criticize their colleagues.

As Stanley demonstrates, it was no accident that Einstein eventually became such a political and cultural icon, or that General Relativity entered popular culture as the theory almost no one could understand, for this was the direct, if in part unintentional, result of Eddington's labors. The war had hindered the international reception and knowledge of General Relativity, which was of course very demanding mathematically. Eddington decided to take up the cause of verifying the theoretical predictions of the German physicist Einstein—whom he had never met—to show how science could triumph over nationalism and hatred. Eddington had thereby recognized not just the scientific but also the political and social significance of Einstein's theory.

Einstein had predicted that gravity bends light, and that this could be observed during a solar eclipse. Eddington seized upon this as his opportunity to demonstrate international scientific cooperation between enemy nations, working hard to organize and finance an expedition. Once in the field, he struggled with the weather and local conditions, setting up telescopes in Brazil and on Principe Island off of the west coast of Africa. As Stanley explains, this was not simply a matter of running an experiment, getting data, and convincing scientists. First of all, Eddington prepared the ground by stoking interest in Einstein's theory and the expedition. When the experimental verification was announced to a large audience crammed into the rooms of the Royal Society, Einstein was compared to Isaac Newton, perhaps the greatest compliment an English physicist could give. The news had already leaked to Einstein, who when asked what he would have done if there had been no confirmation famously responded: “I would have to pity our dear God. The theory is correct all the same” (283). Scientists were stunned at the broad public interest in Einstein and relativity. The physicist's politics made him a hero whom people in the Entente nations could embrace, while the fact that the science was beyond most peoples' comprehension added to his mystique.

The demonstration of light being bent by gravity became a symbol of German-British solidarity, overcoming even the bitterness of war, because Eddington worked hard to craft it that way. In turn, this symbolism was possible because Einstein had chosen to fight against militarism in German science. As the author argues, science is connected to the wider world, including politics, religion, and culture. The values and goals chose for science matter.