Physicists at the world’s big particle accelerators are searching for the God particle. If you saw the movie “Angels and Demons” or listen to Rush Limbaugh, you know that some people, in fiction and in reality, take that language seriously.
Are those who are trying to find this particle really looking for evidence of God? Or would such a discovery put God out of business?
Most physicists don’t like the name “God particle.” They prefer to call the object of their search the Higgs particle, Higgs boson or just “the Higgs.” (To state the obvious, the Higgs or the God particle doesn’t mean that only one such particle exists. The terms refer to classes, not single entities.)
It’s predicted by some theories (first by Peter Higgs in 1964), and if it turns out to be real it will explain important things about the world. Because of its significance, Nobel laureate Leon Lederman nicknamed it “the God Particle” in a book with that title.
Humor is good but in this case it’s given some people a misleading idea of what scientists are trying to accomplish.
So what are they trying to find? What will the Higgs explain — if it turns out that such a thing exists? Most popular explanations are content to say that the Higgs field with which the particle is associated would explain why particles have mass. OK, but let’s try to get some further insight.
Seeking a unified theory
When I was a physics student in the early ’60s there were thought to be four basic forces in the universe. Gravitation and electromagnetism had long been known, but in the 20th century the strong force, which holds the atomic nucleus together, and the weak force, responsible for one type of radioactivity (beta decay) were discovered.
These forces were associated with fields that extended through space-time. Quantum theory shows that excitations of these fields will behave like particles, “quanta,” and forces are described in terms of exchanges of these quanta. The quantum of the electromagnetic field is the photon, which provides the quantum mechanical description of light. Having four basic forces is unsettling for those who seek an elegant unitary picture of the world. Albert Einstein and others tried unsuccessfully for years to find a unified field theory that would combine gravitation and electromagnetism as aspects of a single force. In the ’60s the focus turned to the electromagnetic and weak forces. In fact, Enrico Fermi developed the accepted theory of the weak force by analogy with the quantum mechanical electromagnetic theory. But there were also big differences between the two.
The weak force is much feebler than electromagnetism. In addition, the range of the two forces is very different. The range of electromagnetic forces has no known limit — galactic magnetic fields extend over hundreds of light years. The range of a force is inversely proportional to the rest mass of its quantum and the photon has zero rest mass. (Photons are never at rest but always move at the speed of light, and so have energy.) The weak force, on the other hand, has a range shorter than the size of an atomic nucleus, so its quanta must be very massive. Thus it’s hard to see how the photon and the “weakons” could be related.
Importance of symmetry
Now the idea of symmetry, always important in physical theories, comes into play. Some symmetries are easy to picture. A perfectly round ball has spherical symmetry since it’s not changed by rotations about its center. Other symmetries are more abstract. Electromagnetic fields have a symmetry called gauge invariance, a mathematical generalization of the fact that nothing physical changes if we add the same constant value to the electrical potential everywhere. This symmetry is closely connected with the fact that the rest mass of the photon is zero.
This gauge symmetry could be broadened even further to include more fields in addition to electromagnetism, “gauge fields” that had some of the properties needed to describe the weak force. That suggested a way to unify the two forces, but there was a serious problem. The quanta of such a field for the weak force would have no rest mass, just like the photon, and thus, it seemed, couldn’t correspond to the massive particles that should carry the weak force.
But theorists could appeal to the “Higgs mechanism.” The gauge fields are allowed to interact with another type of field whose average value does not vanish in the vacuum. (Quantum vacuums are subtler and richer than emptiness.) If the symmetry of this new Higgs field is spontaneously broken and part of it takes on definite form, then quanta of some of the original gauge fields acquire mass. They can be identified with particles that transmit the weak force, positively and negatively charged W particles and a neutral Z, all quite massive. The photon remains as the massless quantum of electromagnetism and a massive new particle of a different type, the Higgs, appears.
Well, it hasn’t actually “appeared” so far. Ws and Zs were detected in accelerator experiments in 1983, indicating that this electroweak theory is on the right track, but the Higgs hasn’t been observed yet. That hasn’t stopped theorists from going further and trying to include the strong force (which acts between quarks and is carried by gluons). Those theories haven’t yet achieved the degree of success as electroweak unification. Most particles physicists expect the Higgs to be found. (Ignore rumors that one made in an accelerator experiment would travel back in time and destroy the accelerator before it could be made!) Of course there’s a possibility that it won’t be found — an example of Thomas Huxley’s statement about science being an affair of beautiful theories slain by ugly facts.
I hope I have given a sense of not only the complexity but also the beauty of the theory. If you want a simplified picture, think of the Higgs field as a fluid that fills space. Otherwise massless particles encounter resistance as they move through the fluid and so appear to acquire inertia — that is, mass.
What about the “God particle” business? Even a sketchy understanding of the physics should convince one that it is a misnomer. The Higgs mechanism fails to be godlike because it doesn’t give rise to, or explain, everything. We need to have gauge fields to start with, and most notably the mechanism doesn’t explain its own existence! Every scientific theory has to start with unproven assumptions.
There are some educational opportunities here that you might pursue. God particle language in popular articles offers an opening for discussions about the meaning of “God” and “creation.” Discussions in an adult forum (perhaps with the help of a knowledgeable physicist) could help people get a sense for the interplay of abstract theorizing and experimental work and for the grand scope as well as the limitations of science. And the ideas sketched here are important for theories about the early universe.
Leon Lederman (with Dick Teresi), “The God Particle: If the Universe Is the Answer, What Is the Question?” (Delta, 1993) is a good survey of the development of particle physics from the ancient Greeks to the date of publication. You will have to decide whether you like Lederman’s brand of humor. Lisa Randall’s “Heart of the Matter” (Discover, October 2009, p. 43), discusses the current state of the search for the Higgs and other possibilities at the Large Hadron Collider near Geneva, Switzerland.