In the summer of 1922, Albert Einstein was getting ready to leave Berlin forever. The German foreign minister, Walther Rathenau, had just been shot in broad daylight, largely for being a Jew, and although many Germans were dismayed, some conservatives thought it was a wonderful thing.

Einstein himself was in danger. Already nationalists had held rallies against his ‘Jewish science’, and he had been warned that he was ‘supposedly among the group of persons being targeted by nationalist assassins’. There was a gyrocompass factory in Kiel where he could get a job, and he began to enquire about the pay. ‘He just had the feeling: get away from here to work in tranquility,’ his wife, Elsa, wrote.

But would leaving Berlin for good be right? Before long Einstein changed his mind. ‘He realized’, Elsa explained, ‘that this thing with tranquility is an illusion.’ His Japanese publisher had long been offering him a trip to Japan, and following some negotiations about expenses they settled on a