Just before the start of the First World War, Robert Millikan, professor of physics at the University of Chicago and a specialist in electron theory, travelled to Germany to present an academic paper. A few years earlier, in 1905, the scientist Albert Einstein had proposed a linear relationship between the wavelength of light and the maximum velocity of electrons emitted from irradiated metal. Einstein was developing quantum theory – and Millikan was adamant that he was wrong.

While visiting Dresden Millikan was introduced to a young researcher who had just completed his PhD. The young man was South African and could thus speak English – which is probably why he was asked to show Millikan around campus. They also shared a research interest, as the young researcher was also working on Einstein’s theory.