Facts of the matter

A fascinating study by an Australian physicist of how the quest for deeper understanding of particle physics has shaped 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 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 Australian physicist Suzie 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. The question of how cathode ray tubes emitted X-rays led to the seminal discovery in 1897 of the electron – the first subatomic particle. Atoms were no longer regarded as the smallest indivisible entity in nature. The next century would reveal a whole catalogue of particles, utterly transforming our understanding of matter. The key question for Sheehy is: “What is matter, and how does it interact to create everything around us – including ourselves?” She describes her work, in which she tries to answer this question by studying the tiniest constituents in nature and the forces that govern them, as “one of the most awe-inspiring, intricate and creative adventures that humans have ever embarked on”. Her specialism is accelerator physics, a field that deploys some of the largest machines ever invented to manipulate matter on a tiny scale. An esoteric field, you might think, one that has little relevance to our everyday lives. But as she shows, particle physics has changed how we live dramatically over the past century. Your nearest hospital almost certainly has a particle accelerator, your smartphone relies on quantum mechanics, and Tim Berners-Lee invented the world wide web to help scientists share the vast amounts of data produced by particle experiments. Sheehy is not a theoretician; rather she is an experimental physicist who designs equipment that pushes the limits of technology and generates new data and questions. It’s demanding work requiring curiosity, passion and tenacity. In her book – which is often complex yet never less than fascinating – she uses 12 experiments to show how particle physics has shaped our understanding of the world. She begins with Röntgen’s discovery, before moving on to early experiments showing that the atom was composed mostly of empty space, with a dense nucleus surrounded by electrons, and on to the creation of the first particle accelerators in the 1930s. After the success of the top-secret Manhattan Project to build an atomic bomb during the second world war, physicists embraced a large-scale, collaborative approach. This was the beginning of Big Science. Gone were the days of lone researchers, like Röntgen, toiling away in their laboratories – physics was now about gigantic, expensive machines, designed by groups of experimental scientists, maintained by specialist engineers, and operated by a dedicated staff. Results were interpreted by teams of scholars around the world. These methods yielded a deluge of new particles. The quest culminates – for now at least – with the Large Hadron Collider at Cern, 100 metres below ground near Geneva. Its task was to detect a single and very elusive particle – the Higgs boson, predicted in 1964. The goal was achieved in 2012, thanks to the collaboration of half of the world’s 13,000 particle physicists. In the end, as Sheehy tells us, physics is not just about the search for how the Universe works: “Physics is all about people.” Her journey through the history of particle physics reveals the extraordinary ingenuity of experimental scientists and their selfless dedication to answering big questions about matter and the universe. It is a field that has brought huge benefits to humankind, from new medical imaging technologies to cancer treatments. But in the end, it may well be the physicists’ example of working together to solve problems that will prove the most valuable to us all, at a time when the world faces unparalleled challenges. As Sheehy says: “There is nothing more powerful than humans who come together in collaborative endeavour.”