Mapping the micro-universe

Sscience always requires leaps of faith, but nowhere more so than in particle physics. Since its earliest days it has sought evidence for entities that are not only far too small to see, but might not exist at all. This enterprise has demanded ever more gargantuan and expensive apparatus. Yet as the physicist Suzie Sheehy shows in this engaging and thoughtful book, such punts on the possible have not been reckless investments so much as demonstrations of how curiosity can drive knowledge and innovation.

Take the neutrino. This fundamental particle was postulated in 1930 by the Austrian physicist Wolfgang Pauli to explain a type of radioactive decay of atomic nuclei. He argued that the hypothetical neutrino would have neither mass nor electric charge, and would barely interact with other particles at all. In theory it would pass through layers of lead several light years thick. To suggest such a particle, nigh on inaccessible to experimental verification, was, Pauli admitted ruefully, “a terrible thing”.

Despite the putative neutrino’s elusiveness, physicists went hunting for it anyway. The American scientist Frederick Reines teamed up with the chemical engineer Clyde Cowan to devise neutrino detectors consisting of vast vats of liquid, within which an incredibly collision of a neutrino with an ordinary atom might generate a tiny flash that would be picked up by light detectors . In 1955 this apparatus was installed in an underground basement (to shield it from false signals caused by cosmic rays) near a nuclear reactor, which was expected to be a strong source of neutrinos. By comparing the detections from hundreds of hours of data when the reactor was switched on and off, the duo confirmed that the neutrino is real. Reines won a Nobel prize in 1995 for his efforts; Cowan died before that recognition came.

This is a common pattern in particle physics: a new particle is predicted on theoretical grounds to resolve some puzzle, then an elaborate effort is launched to detect it. That was the story for the celebrated Higgs particle, detected in 2012 in the Large Hadron Collider at the European particle-physics laboratory CERN, near Geneva, by smashing protons (subatomic components of the atomic nucleus) into one another as they circulated in a ring -shaped accelerator at within a whisker of the speed of light. The Higgs particle was predicted in the 1960s by the British physicist Peter Higgs and others to explain how other acquire particles their mass. It took many decades, and a lot of money, to verify that prediction, which completed the inventory of known particles and forces. Called the standard model, this roster includes such particles as the muon, which don’t appear in atoms at all and therefore initially seemed surplus to requirement. “Who ordered that?”, one Nobel laureate asked when the muon was discovered in 1936.

Physicists know that the standard model can’t be the whole answer to the question of what the universe is made of. There seem to be types of matter and energy that the model doesn’t include, such as the dark matter that holds galaxies together and seeded the formation of large-scale structure in the universe—but which is even more aloof than the neutrino. The standard model also leaves some puzzles unanswered, such as why there seems to be more matter than antimatter in the universe. So the quest now is to find cracks in the model that might point to “new physics” – entirely new particles or forces that might reveal the next layer of reality. Whether existing accelerators can show us that remains to be seen. There was great excitement when, this April, a close analysis of ten-year-old data from the now defunct Tevatron collider at Fermilab, near Chicago, showed an apparent discrepancy with the standard model’s predictions for the mass of another fundamental particle. But such anomalies have been claimed before, and particle physicists know from bitter experience how carefully they must be checked to rule out mundane sources of error or spurious signals.

The Matter of Everything is a fine survey of the story of particles, from the discovery of the electron in 1897 to the Higgs and beyond. Some of this story, especially the early days of Ernest Rutherford splitting the atom and of the invention of particle accelerators by John Cockcroft, Ernest Walton and Ernest Lawrence, has been told several times before. But Sheehy’s account excels in two respects. First, she gives as much emphasis to the engineering as to the physics, showing just how difficult it is to build these devices and how much ingenuity and creativity (as well as hazard) is involved. From skilled glassblowing to the invention of superconducting magnets, high-energy physics pushes the technologist’s art to the limit. Second, she shows that every discovery, no matter how exotic and recondite it might seem, has produced valuable spin-offs, from medical applications such as cancer treatments and imaging methods such as PET scans and fMRI to the very technology enabling some of you to read this piece: the World Wide Web, initiated by Tim Berners-Lee at CERN. What’s more, Sheehy spots some of the many contributions of female scientists in a field that is still overwhelmingly male-dominated: a disparity that Sheehy, a researcher at Oxford and Melbourne, is herself helping to change.

It’s one of the peculiarities of particle physics that its instruments have needed to become ever bigger in order to explore events at ever smaller scales: inside the atom, then inside the proton, and now still deeper. The first prototype cyclotron – a particle accelerator that sends the particles in spirals as electric fields speed them up – was made by Lawrence from a copper tin about five inches in diameter, sawn in half. The Large Hadron Collider – not a cyclotron but a synchrotron, in which the particles’ paths are confined to a circle – has a circumference of 27 kilometres. In 2019 the European Strategy for Particle Physics included a proposal for a 100km-long synchrotron.

This expansion in scale and cost meant the style of the science had to change. Such devices certainly exceed the means of a single research group or even a single institution, and have to be national or international projects used by vast teams of researchers. “By the 1950s an experiment came to entail a gigantic piece of machinery designed by one group, maintained by specialist engineers, operated by dedicated staff, the results of which were analysed by one team and interpreted by yet another”, Sheehy writes. This is industrial-scale science, involving teams of hundreds, many of whom will focus on one small part of the problem – a specific set of calculations, say. It could hardly be further from the ultra-low-budget sealing-wax-and-string philosophy that enabled Rutherford to discover the atomic nucleus and split the atom.

Managing the huge teams is a skill in itself. Research (“beam time”) on these unique and oversubscribed devices is precious, assigned by committees often years in advance of an experiment. This means it becomes harder to countenance high-risk projects: the system favors caution and conservatism. Typically there is a consensus about what the most pressing questions are, and everyone pursues those. It is hard to see an alternative if particle physics is to happen at all – but the compromise needs to be recognized.

Its disproportionate scale means that particle physics fosters resentment. Perceived by some other physicists as insular, it nevertheless attracts generous funding and dominates the headlines, to the extent that many outsiders think smashing particles together is all that physicists do. Those tensions came to the fore in 1993, when plans for a new accelerator called the Superconducting Super Collider (SSC), construction of which had already begun in Texas at a cost of around $3 billion, were canceled because of rising costs, mismanagement and the Fading of a Cold War is imperative to demonstrate scientific supremacy. Some scientists, including other physicists, persuaded the US Congress that the funds could be better used elsewhere. Had it been completed, some believe the SSC might have discovered the Higgs particle before CERN did.

There are surely difficult questions to be asked when the costs of the facilities are so high. Particle physics is inherently speculative, but as the SSC’s opponents argued, that does not mean its every dream should be indulged. Yet although Sheehy compellingly argues that the spin-offs from this curiosity-driven research have been substantial, it would be intellectually myopic to make that the sole justification. When, in 1969, the former Manhattan Project physicist Bob Wilson was implored by a US senator to find some national-security value for the proposed new accelerator that became Fermilab, he replied that “it has only to do with the respect with which we regard one another, the dignity of man, our love of culture … It has nothing to do directly with defending our country except to make it worth defending.”

Philip Ball is a science writer. His latest book, The Book of Mindswill be published this month

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