Encounters With the God Particle
The Higgs boson, the pope, and the curious interaction between organized religion and big science
This is the season when many minds are tuned in to the concept of “God” and origins and fundamentals. I am reminded of a papal visit in the spring of 1982, when Pope John Paul II came to CERN, the European center where I was engaged in physics research on basic physical law. He spoke [1] to the staff about “prodigious things,” world peace, and how he hoped the science discovered at CERN should be subject to the constraints of conscience, quoting Genesis 1:31 (“And God saw everything that he had made, and behold, it was very good”). In reply, the CERN director spoke of a fecund dialogue between science and religion. I am sure most of my colleagues—a good portion of them Jewish, many European agnostics, many Catholics—kept these two categories in separate mental compartments. But undoubtedly the need for good public relations on CERN’s part and the need for an open mind on scientific research on the church’s part played some role in this curious interaction between organized religion and big science.
Up to the middle of the last millennium, of course, with the exception of some considerable accomplishment by the ancient Greeks, the search for rules that govern that physical universe was largely religious in nature. But around the time of Galileo things took a fruitful turn. The search for physical law became more of a game of proposition, prediction, and test by experiment. We accepted a modus of working on what was accessible to our instruments or detectors. We went after laws at large scales—Newton’s gravitation, say, or the laws of friction. We studied and systemized electricity and magnetism. We learned about atoms and with the additional knowledge of electrical forces got access to the laws of chemistry. By the end of the 19th century we were breaking down atoms, learning over a 50-year span about the construction of the nucleus and sub-nuclear structure.
Physics experiments today are often done by colliding constituents of matter with one another at ever-higher energies and studying the debris. The highest-energy facilities—today, as then, at CERN—are huge and expensive, but they work at the frontier of the research that led us this summer to the much-noted [2] announcement [3] of the discovery [4] at CERN of the so-called “god particle,” a particle associated with how all other particles get their masses. (In fact, the phrase “god particle” does not convey much information, but it is a fine way to attract attention, and it helped to sell a 1993 book [5] when it was coined.) The “god particle” is only one piece of an elaborate structure known as the standard model.
The basics of the so-called quantum field theory—the theoretical context in which the Higgs boson resides—are spectacularly beautiful.
Physicists prefer the term Higgs boson to “god particle.” That title, after one of several theorists who around 1964 more or less simultaneously proposed a mechanism that implies its existence, does have significance for those who know the science. The CERN discovery was not a matter of blind luck, like that of a gambler discovering a row of five cherries on a slot machine. The invention and search for the Higgs boson are part of the next stage of physics research, where we attempt to learn the rules that govern the sub-constituent parts of the nucleus and other stable or unstable particles and give us a coherent picture of the basic rules governing the way the universe was, is, and will be. In fact, there remains much to do to confirm and test whether what was found was really the Higgs boson, as well as to continue to sift through the various ways this particle fits into our larger conceptual framework about matter. The machine that discovered the Higgs boson at CERN has a physical scale of tens of kilometers and costs many billions of dollars—so expensive that politics killed a counterpart machine [6] here in the United States after much money had already been spent.
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All the thought and experience about physical law of the last 500 years have given us a set of criteria as to what makes a good set of rules. For one, the language of physical law is mathematical. Why this is so is a mystery. Mathematics carries within itself a kind of logic that somehow is reflected in the way the world is. And it has to be the right kind of mathematics. Newton discovered his laws of gravitation with the aid of calculus, which he essentially had to invent on his own. It was short work with his mathematics in hand. He then spent years trying to explain these laws with a geometrical description adapted to the knowledge of his contemporaries.
Furthermore, a set of rules at a small scale should encompass and explain the laws at larger scales. The rules must have testable predictive power. The rules must be simple and economical. And the rules must be aesthetic. The basics of the so-called quantum field theory—the theoretical context in which the Higgs boson resides—are spectacularly beautiful. That is the only way to put it, a beauty based on what is almost an inherent inevitability—“almost” because rival theories are in play, each with its own kind of beauty.
So, what makes the Higgs boson so important? The Higgs mechanism was put forward in the 1960s as a way to allow symmetry in the underlying structure of a theory while the physical manifestation of the theory did not exhibit such symmetry. Physicists were coming to realize that symmetries play a central role in physical law—a realization that had taken root over 50 years earlier. Then, in 1967, a group of theorists found a way to use the Higgs mechanism to unify two previously separate domains of subatomic forces, electromagnetism and the so-called weak interactions. (The latter were responsible for some radioactive decays.) This “electroweak unification” fit the set of rules I wrote above with one particularly grave set of exceptions: When you tried to calculate with them, you apparently came up with meaningless numbers, infinities. But by the early 1970s other workers had learned that the apparent infinities were only apparent. In fact when you were careful to calculate more completely and look at only physically measurable quantities, the infinities would systematically cancel out.
The Higgs mechanism also did something else: It put terms into the equations that were identical with terms that corresponded to the various particles having been given individual masses by hand. The mass of an object is a measure of the difficulty of speeding up or slowing down that object: Up until the invention of the Higgs mechanism, mass was just something you had to take as an otherwise unjustified given. With the Higgs mechanism in play, mass has a significance, an origin. Since mass is one of the most fundamental concepts in physical law, the Higgs mechanism, and the Higgs boson associated with this mechanism, becomes a central piece of our picture of the rules.
In fact the electroweak unification predicted three new and very heavy particles, and, even better, information on their mass ratio was numerically predicted. When Pope John Paul II visited me and my co-workers at CERN, a new machine had begun operation, and the discovery of these new particles, with exactly the predicted properties, was less than a year away. What remained was the discovery of the Higgs boson itself, which would eliminate alternative theories and cement the new interpretation of mass. Now, 30 years later, the Higgs boson is on the road to being fully confirmed.
During Pope John Paul II’s visit, Director-General Herwig Schopper presented him with a representation, made in the CERN workshops, of a high energy proton-antiproton interaction, such as was seen in the SPS collider. June 15, 1982. (CERN)
I admit to a certain melancholy about all this. When I passed through CERN in 1982, I had been thinking about physics for some 15 years. At the beginning of that period, it was still possible for a professor and several graduate students to perform an experiment at one of the existing accelerators and get a result worth publishing, even to make a major discovery, in a matter of months. Theorists could both propose and analyze on the same time scale. By the early 1980s things had changed. Experiments in the new era involved bigger and bigger detectors. Bigger and bigger collaborations were necessary, and the time required to do an experiment grew longer. The accelerators, ever more expensive, were fewer, and their construction took years and involved dodging political minefields.
I am not complaining about the cost here. (I admit I did not build the machine myself.) The track record of something falling out of research on “pure” physics is pretty good. The World Wide Web arguably came from CERN, and techniques for the difficult analysis of the vast amounts of data from high-energy collisions are paying good dividends in other contexts. The current generation of accelerators has also taught us a great deal about superconducting technology.
But the fact that the United States has not provided an equivalent machine to check CERN’s results—or even to have beaten them to the punch—is discouraging. Will experiments at a single machine, without a second machine to check the results, be acceptable? This is not going to get any easier. Peter Higgs had to wait 50 years to learn that his proposal was at least partly proven right. He retired in 1996 and is now in his early eighties. Results from modern machines come slowly, and many theorists have wandered off into regions where unverifiable speculation is king. For the worker bees who stick to experimentation, thousand-person collaborations are now the rule. Will the most creative individuals be willing to spend all their time in such collaborations on a single life-spanning experiment? I wouldn’t bet on it.
Perhaps the popes still have something to teach us.
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