De Broglie’s towering achievement

The French physicist Louis de Broglie was descended from a noble family - his great-great-grandfather was guillotined in the French Revolution and the physicist held the courtesy title of ‘prince’ for most of his life until he succeeded his elder brother as the 7th duc de Broglie in 1960. De Broglie’s first degree was in history, but he developed an interest in science whilst serving in the French Army. During the First World War, he served as a combat engineer and spent some time working at a radio communication post established in the Eiffel Tower. Remarkably for someone without a background in physics, he proposed the ground-breaking idea that particles have a wave-like nature. He derived the formula for what came to be known as the de Broglie wavelength in his PhD thesis. Whilst, in retrospect the value of his research is clear, his examiner Paul Langevin (who worked on magnetism and proposed the twin paradox), was not sure whether the young physicist’s work was sufficiently significant to be awarded a doctorate. Langevin sent de Broglie’s thesis to Einstein for another opinion. Einstein responded that de Broglie’s work should certainly pass. Despite his distaste for quantum theory, Einstein described de Broglie’s idea as “a first feeble light on this worst of physics enigmas”