The Accidental ParticleThey're turning on the Large Hadron Collider. Don't expect the Higgs boson to show up.
Posted Tuesday, Sept. 9, 2008, at 6:56 AM ET
The first particle beams will race through Switzerland's Large Hadron Collider, the biggest particle accelerator ever built, this Wednesday. After 15 years—and something like $8 billion in construction costs—the machine should start producing early results by midfall. According to the usual story, particle physicists everywhere are anxiously awaiting evidence of an as-yet-unseen elementary particle called the Higgs boson.
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StumbleUponLast summer, I argued that the discovery of the Higgs could spell disaster for the field. If we find the Higgs, the Standard Model of high-energy physics would provide a theoretical account of all known particles and their interactions. Physicists could use it to predict the results of every particle accelerator experiment ever performed with near-perfect accuracy, given a big enough computer. But the Standard Model isn't intuitive enough to provide insight into why the world happens to be the way it is. Most physicists hope that there's a deeper, more revealing theory waiting to be discovered; if all the LHC finds is the Higgs, they will be sorely disappointed. Fortunately—and this I didn't mention last year—there's no particular reason to expect that the Higgs will show up.
That the Higgs boson appears in the Standard Model at all is more a matter of historical and sociological coincidence than a prediction based upon firm scientific data. Indeed, there is no direct (or indirect) proof that the Higgs boson is real. The hodge-podge of theories that are rolled up in the Standard Model are such that everything we think we know about particle physics may be exactly right—and yet the "God particle" could be a fiction.
The story of the Higgs boson goes back almost 50 years, to when the theories that would ultimately be combined into the Standard Model were first developed. At that time, physicists were aware of three apparently distinct forces that could influence the motion of particles: the electromagnetic force, responsible for familiar phenomena like thunderstorms and televisions, and two other forces that were important in nuclear processes, known as the strong and weak forces. They knew of a fourth force, too—gravity—but it was far too weak to be important in these experiments.
The Higgs saga begins in 1960 with a physicist named Sheldon Glashow, who had just wrapped up his Ph.D. at Harvard and was working in Copenhagen, waiting for a visa to come through so he could begin his postdoctoral work in Russia. Glashow had a hunch that two of the three forces—electromagnetism and the weak force—were actually manifestations of the same thing, an "electroweak" force. In 1961, he published a paper that tried to describe both forces with a single mathematical framework.
But there were problems with Glashow's theory. When two electrons exert a force on each other, that force is "carried" by a different kind of particle that travels between them. Electromagnetism, for instance, is carried by photons, the same stuff that makes up light; when two electrons repel each other, they exchange photons. To make the connection with the weak force, Glashow needed to suppose that there was a kind of analog to the photon that would carry the weak force. But no one had ever seen a particle like this, and if they were really anything like photons, they should have been very easy to observe.
One way around this problem was to suppose that the weak-force carriers were very heavy. The heavier a particle is, the bigger the accelerator you need to produce it; by theorizing large masses for these force carriers, it was possible to put them outside the range of 1960s technology. This would have explained why no one had seen them, but it also threatened to make Glashow's theory untenable: The only mathematically consistent way that anyone knew of to make these new force-carrying particles so heavy involved adding a new, very light particle to the theory called a Goldstone boson. (A boson is one of two types of particle—the others are called "fermions"—distinguished by differences in their internal rotation. Photons are bosons; electrons are fermions.) These Goldstone bosons would have been easy to detect if they were real, again because they're so light. Yet they were conspicuously absent in experiments.
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