In 1895, the German physicist Wilhelm Roentgen noticed that a phosphor-coated screen emitted green light when exposed to a cathode ray tube. He quickly realized that he had found a new invisible ray. When asked what he was thinking when he saw that green light, he replied, “I wasn’t thinking. I was investigating.” In fact, he spent seven weeks researching, locked in his lab, only emerging when his wife Anna insisted he eat something. He rewarded her concern for his well-being by using the unknown rays to take a picture her hand on a photographic plate. It proved they could travel through skin and flesh: the plate revealed their bones and wedding ring. When she saw the picture, she was horrified and said: “I saw my death!”
In his notebook, Roentgen identified the unknown rays with a letter: “X-rays”. As Sheehy says, this is “possibly the best unintentional branding in the history of physics.” Within a year of its discovery, X-rays were being used to find shrapnel in the bodies of soldiers on the battlefield.
The question of how cathode ray tubes emit X-rays led to the groundbreaking discovery of the electron – the first subatomic particle – in 1897. Atoms were no longer considered the smallest indivisible unit of nature. In fact, the next century would reveal a whole catalog of particles and completely change our understanding of matter.
The key question for Australian physicist Suzie 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 using the smallest parts of nature and the forces that control them, as “one of the most impressive, intricate and creative adventures that man has ever embarked on”.
Her specialty is accelerator physics, a field that uses some of the largest machines ever invented to manipulate matter on a tiny scale. An esoteric field, one might think, that has little meaning for our everyday life. But as she shows, particle physics has dramatically changed the way we live in the last 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 generated by particle experiments.
Sheehy is not a theorist, not a modern day Einstein making speculative hypotheses about the nature of reality. Rather, she is an experimental physicist who designs devices that push the boundaries of current technology and generate new data and questions. It is demanding work that requires curiosity, passion and tenacity.
In her often complex, but never less than fascinating book, she uses 12 experiments to show how particle physics has shaped our understanding of the world we live in. She begins with Roentgen’s discovery before moving on to early experiments showing that the atom was mostly empty space with a dense core surrounded by electrons, up until the development of the first particle accelerators in the 1930s.
After the success of the top-secret Manhattan Project to build an atomic bomb during World War II, physicists decided to take a large-scale, collaborative approach. This was the beginning of Big Science. Gone were the days of lone researchers like Roentgen toiling in their labs—physics now revolved around huge, expensive machines designed by groups of experimental scientists, maintained by specialized engineers, and operated by dedicated personnel. The results were interpreted by teams of scientists around the world. These methods yielded a flood of new particles, from pions to positrons.
The search culminates – at least for now – in the Large Hadron Collider at CERN, a 27 km long circular proton collider, 100 meters underground near Geneva. Construction took two and a half decades and was overseen by Welsh physicist Lyndon Evans, affectionately known as Evans the Atom.
Sheehy, who worked at CERN, guides the reader through this triumph of technical and scientific collaboration, “one of the greatest experiments ever built.” Dubbed the largest machine on earth, it is so sensitive that it must be corrected for incredibly small effects, such as the movement of the earth’s crust by the sun and moon or the passage of high-speed trains – all of which perturb proton orbit.
A proton is a million times smaller than a grain of sand. The LHC “delivers two beams of hundreds of billions of protons at 99.999999 percent the speed of light, focuses them to less than the width of a hair, and then collides them.” His task was to discover a single and very elusive particle – the Higgs boson, predicted in 1964. This goal was achieved in 2012 thanks to the collaboration of half of the world’s 13,000 particle physicists and drawing on the resources of 110 countries.
Ultimately, as Sheehy tells us, physics isn’t just about finding out 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 devotion to the Answering big questions about matter and the universe. It’s an area that has brought tremendous benefits to mankind, from new medical imaging technologies to cancer treatments. But in the end, it could well be the example of physicists working together to solve problems that will prove most valuable to all of us at a time when the world is facing unprecedented challenges. As Sheehy says, “There is nothing more powerful than people banding together in a common effort.”