How the quest for a deeper understanding of particle physics has transformed the way we live

In 1895, the German physicist Wilhelm Röntgen noticed that a phosphor-coated screen gave off a green light when exposed to a cathode ray tube. He quickly realised that he’d found a new invisible ray. Asked what he thought when he saw this green light, he replied: “I didn’t think. I investigated.” In fact he spent seven weeks investigating, locked away in his laboratory and only coming out when his wife, Anna, insisted he eat something. He rewarded her concern for his wellbeing by using the unknown rays to make an image of her hand on a photographic plate. It proved that they could travel through skin and flesh: the plate revealed her bones and wedding ring. When she saw the image, she was appalled, saying: “I have seen my death!”

In his notebook, Röntgen used a letter to denote the unknown rays: “X-rays”. As Sheehy says, this is “possibly the best unintentional branding in the history of physics”. Within a year of his discovery, X-rays were being used to find shrapnel in soldiers’ bodies on the battlefield.