Book Reviews - Winter 2023

Quark of Habit

Scientists keep pushing for larger particle colliders—but is this really wise?

By Sabine Hossenfelder | December 1, 2022
Har Gobind Singh Khalsa (Flickr/ gobindkhalsa)
Har Gobind Singh Khalsa (Flickr/ gobindkhalsa)

The Matter of Everything: How Curiosity, Physics, and Improbable Experiments Changed the World by Suzie Sheehy; Knopf, 320 pp., $30

Around 400 BC, the Greek philosopher Democritus proffered the idea that all matter was composed of indivisible, featureless constituents. He described them using the Greek word for “uncuttable”: atomos. Two thousand years later, scientists found that Democritus had, at least in principle, been correct. But the particles he envisioned—now called atoms—were neither featureless nor indivisible, but instead were made up of large nuclei surrounded by small electrons. In time, the atomic slicing continued, homing in on the ever-smaller components of the universe: nuclei were actually concentrations of neutrons and protons. And these particles, it turned out, consisted of quarks held together by gluons. How did physicists learn these things? And have we finally uncovered the smallest constituents of matter? Suzie Sheehy tells the story.

Her book is a historical account of experimental firsts, beginning with German physicist Wilhelm Röntgen’s discovery of x-rays in 1895. Dozens of books have been written about physicists’ quest to find a theory for all matter, but Sheehy’s stands out. As an experimental particle physicist, she focuses on the experiments themselves rather than the natural laws derived from them. She takes readers through Ernest Rutherford’s discovery of the structure of the atom in 1911, the development of quantum mechanics, the construction of the first particle accelerators, and the many particles that physicists went on to find. Along the way, we also learn about the discovery of cosmic rays, nuclear reactions, and neutrinos. Sheehy explains the incremental improvements in accelerator technology used to study the behavior of various particles—a story that ends with the success of the Large Hadron Collider (LHC), operated by the European Organization for Nuclear Research (CERN) in Switzerland, and the completion of the Standard Model of particle physics. Sheehy likewise brings to life the heroes behind the discoveries—scientists who stumbled, persevered in the face of failure, coped with inadequate equipment, and endured the ridicule of colleagues.

Unfortunately, Sheehy herself stumbles a number of times in The Matter of Everything. Consider some examples. “Muons have a unique feature, in that they can travel a long way through dense objects,” she writes. Muons are not unique in this regard. “The Standard Model includes all the particles we’ve seen discovered, from the electron … to the quarks and their composite particles: protons, neutrons along with pions.” The composite particles are not part of the Standard Model. And in her explanation of magnetic resonance imaging (MRI), she writes: “As early as the 1940s other physicists had realized that strong magnets could align hydrogen atoms inside the human body.” MRI does not align atoms—doing so would kill the patient; rather, it aligns the spins of atomic nuclei along the axis of the magnetic field. None of these are big slips, but they will leave some readers baffled.

In the first chapters, Sheehy derives a lesson from her expositions, notably that discoveries are often unplanned and their consequences impossible to foresee. But in later chapters, she gives up on drawing conclusions. This is a shame, for there are other lessons to learn. About the problems that can spring up in large communities, for one. The field of particle physics is unique for its huge international collaborations that bring together thousands of scientists and engineers. Yet particle physics, for all of its successes, is also hopelessly split in half between the experimental and the theoretical. Physicists on either side of this divide tend to have a mediocre understanding of the other. I frequently encounter experimentalists, for example, who uncritically repeat the hypotheses of theorists—in effect, investing these hypotheses with a seriousness they don’t necessarily deserve.

Sheehy is no exception. Like every experimentalist I have heard opining on the matter, she casually brushes aside the 2008 lawsuit filed against CERN by a retired American nuclear-safety officer and a Spanish journalist. Together they sought to prevent the LHC, then still under construction, from operating, out of fear that it might create a microscopic black hole. Sheehy writes that cosmic rays routinely create collisions at even higher energies than those being deployed by the LHC, and that if it were possible for a tiny black hole to be created that way, planet Earth and everyone on it would likely have been obliterated long ago. What Sheehy doesn’t mention is that cosmic ray events and LHC collisions have very different center-of-mass systems. The former move rapidly relative to Earth, the latter do not. The major risk was not just a microscopic black hole at the LHC but one that would have gained mass as it passed through Earth, eating up the planet from within. Theoretically, an event like this would be more likely to happen with black holes that move slowly relative to Earth—like those that the LHC might have produced. This didn’t happen, for ultimately, the notion that the LHC would spawn black holes made as little sense as the notion that it would create the particles that make up dark matter, as some physicists had hoped. But the lawsuit wasn’t as frivolous as particle physicists like to think.

Sadly, as Sheehy’s book goes along, it degenerates into a pitch for building a particle collider even larger and more expensive than the LHC. On this count, too, she merely recites unconvincing arguments so often bandied about by experimentalists. Has it never occurred to any of them that past progress might have happened not because of serendipity but despite it, and that relying on serendipity is no longer enough? That building particle colliders at CERN because, in 1989, English computer scientist Tim Berners-Lee invented the World Wide Web there is as useless as constructing patent offices because Einstein once worked in one?

Most disappointing, Sheehy’s stated motivation for creating a bigger particle collider comes in the form of a quotation from someone else, Italian physicist Daniela Bortoletto, who asserts that doing so would be “the best way to make progress” on understanding dark energy and dark matter. This statement—highly questionable, if not simply wrong—is not explained any further.

Some research endeavors come to an end: we have, for example, discovered all continents on Earth and all organs in the human body. I think it’s about time that particle physicists take seriously the possibility that their endeavor has come to an end, too. Meanwhile, The Matter of Everything will give you a good idea of how experimental particle physicists think.

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