CERN is the largest particle physics laboratory in the world. And, ironically, it has to be to study the smallest things in nature. Located near Geneva, its buildings straddle the border of France and Switzerland. As part of Alan’s quest to explore the biggest and smallest things we know of, CERN was a must-visit location. Thanks to Sarah Charley, we met both experimentalists and theoreticians working with the giant ATLAS and CMS detectors, while carefully observing masking and other pandemic safety precautions—which is why Alan spoke with Director-General Fabiola Gianotti outside, in the so-called “detector graveyard.”
Written by Alan Lightman
The acronym, CERN, comes from the French Conseil Européen pour la Recherche Nucléaire, translated as “The European Organization for Nuclear Research.” CERN is a behemoth facility with a circular tunnel 27 kilometers in circumference. Using electric fields to accelerate charged subatomic particles faster and faster as they go round and round the ring, and with enormous magnets to bend the particles’ trajectories into circles, CERN can accelerate subatomic particles up to 99.999999% the speed of light. Founded in 1954, CERN includes 23 member countries.
The holy grail of physics has always been to discover and understand nature’s fundamental forces and particles. Before 1897, when J.J. Thomson discovered the electron, it was thought that the atom was the smallest thing in nature. Since then, we have found that there are particles much smaller than atoms.
Today, we know of four fundamental forces: gravity; electromagnetism; the strong nuclear force, responsible for holding together the subatomic particles at the centers of atoms; and the “weak force,” responsible for certain kinds of radioactive decay, such as the disintegration of neutrons. In recent years, physicists have found that the weak force and the electromagnetic force are aspects of a more fundamental force now called the “electroweak” force. It is hoped that eventually we will understand all four fundamental forces as manifestations of an even more fundamental single force, a “grand unified” force.
Along with the fundamental forces, physicists have theorized or found several kinds of fundamental particles, which cannot be subdivided into small particles: the graviton, which conveys the gravitational force and which has not yet been discovered; six different quarks (called “up,” “down,” “charmed,” “strange,” “top,” and “bottom”), which create and respond to the strong nuclear force; the gluon, responsible for conveying the strong nuclear force; 3 kinds of relatively light particles called leptons (electrons, muons, and taus); three kinds of neutrinos (the electron neutrino, the muon neutrino, and the tau neutrino); 3 electroweak particles (the photon, the W boson, and the Z boson); and the Higgs particle. Although this list may seem like the inventory of a chaotic zoo, it is far simpler than what physicists were contending with in the 1960s when there were hundreds of new subatomic particles discovered in the high energies of particle accelerators, and physicists were running out of Greek letters to name them all. It has subsequently been found that most of those particles were comprised of the more fundamental particles listed above.
Researchers at CERN were responsible for discovering the W and Z bosons in 1983 and the Higgs boson in 2012. The W and Z bosons were predicted in the 1968 electroweak theory proposed by Steven Weinberg, Sheldon Glashow, and Abdus Salam (all to later receive the Nobel Prize.) These particles convey the weak force responsible for the disintegration of neutrons into protons, electrons, and neutrinos. The W and Z discovery at CERN was led by experimental physicists Carlo Rubbia and Simon van der Meer (who later also received Nobel prizes). The Higgs boson, which is responsible for slowing down particles (and thus giving them an effective mass), acting like molasses filling up space, was predicted in 1964 by a mild-mannered theorist from the University of Edinburgh named Peter Higgs, who had to wait 50 years for his prediction to be vindicated (and to win his Nobel).
One of the current goals of theoretical physics is to explain why particles have the particular masses they do and to put together a theory that combines Einstein’s theory of gravity, called General Relativity, with quantum physics. Such a theory of “quantum gravity” could, in principle, explain how our universe came into being and what came before.