Since the announcement yesterday that scientists working with the Large Hadron Collider have all but certainly discovered evidence of the so-called “God Particle,” much of the world has been scrambling to understand the news. For that, we turned to Kenneth Ford’s 101 Quantum Questions, in which number 98 asks “What is the Higgs particle? Why is it so important?” Ford’s answer—written just last year but now happily showing its age—is below.
Satyendra Nath Bose and Enrico Fermi possess the distinction of having classes of particles named after them [see Question 49: “How did bosons and fermions get their names?”]. But only Peter Higgs, an emeritus professor of physics at Edinburgh University, shares his name with an individual fundamental particle*— a particle that, as of this writing, has yet to be observed. In the early 1960s, particle theorists were united in predicting that if their theories were correct, there should exist in nature a boson of zero charge, zero spin, and zero mass. No such particle was known. If it existed and interacted with other matter as it was expected to do, it could hardly have escaped detection. In 1964 Higgs saw a way out of the conundrum of the expected but unobserved fundamental particle. He discovered within the mathematics of relativistic particle theory (field theory) a loophole, so to speak. This loophole, which has come to be called the Higgs mechanism, permits, or even demands, that this particle have nonzero mass—possibly even a quite large mass (by particle standards). Thus was born the Higgs particle, or, as it is affectionately called, just the Higgs. Like the originally envisioned particle, the Higgs is a boson with no charge and no spin, but its mass could be as much as hundreds of GeV.
Soon new duties were assigned to the Higgs. By the early 1970s, theorists had concluded that the field underlying the Higgs particle might account not only for the mass of the Higgs particle itself, but for the masses of many particles. The Higgs field, filling all of space, is expected to provide a kind of viscosity that impedes particles and gives them mass. This is obviously a highly oversimplified statement, since for all the fundamental particles that do have mass, no two have the same mass, and certainly there is no theory that predicts what their masses should be. Yet at least one oddity in particular might find its explanation in the Higgs. That is the enormous disparity in the masses of the force carriers for the electromagnetic and weak interactions. As discussed at Question 16 [“How far can one particle ‘reach out’ to influence another one?”], theory has united these two interactions of very different strength into a single electroweak interaction, but with one force carrier, the photon, having no mass, and two force carriers, the W and Z particles, having enormous mass. Theorists hold out the hope that the Higgs field may provide not only the “viscosity” that gives the W and Z particles their masses, but also the “cement” that unites these particles and the massless photon.
Scientists have been searching for the Higgs particle for years and are beginning to feel optimistic about finding it with the aid of the Large Hadron Collider, or perhaps even with Fermilab’s Tevatron. Few doubt its existence. It is called the only missing brick in the edifice known as the standard model [see Question 14: “What is the standard model?]. It would be the only fundamental particle with no spin. Almost the only thing we don’t know about it is its mass. The best estimates put its mass at around twice the mass of the W and Z particles, or some 100 to 150 times the mass of a proton. This puts it tantalizingly within range of the Large Hadron Collider.
* Higgs has written and spoken good-humoredly of his “life as a boson.” I don’t know how he feels about having his namesake particle referred to as the “God particle.” This label comes from a book of that name by Leon Lederman (The God Particle: If the Universe Is the Answer, What Is the Question? with Dick Teresi [New York: Dell, 1993]). It is rumored that Lederman, himself a distinguished particle physicist, wanted to call the Higgs particle the “goddamned particle” because it had eluded all attempts to find it, but that his publisher, concerned about public taste, changed it to “God particle.”