Thursday, April 10, 2008

A Ghost in the Machine

Get physicists and cosmologists talking about their work and they will tell you that there are elegant theories and messy ones. Almost all of them believe the universe conforms to an elegant one. A central goal of today's physics, in fact, is to show that at its very beginning, the universe was ordered and unified. But this unity didn't last for long. Just instants after the Big Bang, as the explosion cooled and its contents scattered, the cosmos' forces and matter differentiated. The universe fell from a state of perfect grace into its current complexity, in a cosmic parallel to Adam and Eve.

Many great minds — Democritus, Isaac Newton, James Clerk Maxwell, Albert Einstein — took giant steps toward bringing the universe's lost unity out of hiding. In 1964, Peter Higgs, a shy scientist in Edinburgh, added his name to that list by coming up with an ingenious theory that gave scientists the tools to explain how two classes of particles, which now appear to be different, were once one and the same. His theory proposes the existence of a single particle responsible for imparting mass to all things — a speck so precious it has come to be known as the "God particle." The scientific term for it is the Higgs boson, and to find it physicists are counting on the most powerful particle accelerator ever constructed: the Large Hadron Collider (LHC) at the CERN laboratory in Geneva, a 17-mile underground circuit that took 25 years to plan and $6 billion to build.

The LHC won't begin operation until this summer, but when Higgs, 78, made his first visit there on April 5, it was, in the nomenclature of particle physics, "an event." Grown men and women with Ph.D.s swarmed Higgs for autographs, but he appeared far more taken by the experimental equipment he hoped would find the Higgs boson and thus prove his theory. A particle detector called ATLAS, for instance, is 150 ft (46 m) long, 82 ft (25 m) high, weighs 7,000 tons and is connected to enough cable and wiring to wrap around the earth nearly seven times. "The sheer scale of the detectors was overwhelming," Higgs later said, displaying about as much emotion as you get from this restrained British scientist. Another outpouring: "I suppose I'll open a bottle of something if they find it."

He'll have waited a long time, at least in puny human terms. In 1964, Higgs theorized a mechanism to explain how two types of particle, massless like everything else immediately after the Big Bang, came to acquire different masses as the universe cooled. Using this mechanism, which two Belgian physicists simultaneously posited, scientists were able to extrapolate how all particles get their mass. Higgs thus plugged a major hole in the Standard Model, the far-reaching set of equations on the interaction of subatomic particles that is the closest modern physics comes to a testable "theory of everything."

Working from Higgs' theory, scientists postulate that initially weightless particles move through a ubiquitous quantum field, known as a Higgs field, like a pearl necklace through a jar of honey. Some particles, such as photons — weightless carriers of light — can cut through the sticky Higgs field without picking up mass. Others get bogged down and become heavy; that is the process that creates tangible matter. "The Higgs gives everything in the universe its mass," says David Francis, a physicist on the ATLAS experiment. Pointing at CERN's grand geological amphitheater of the Jura and the Alps. "None of that is possible without the Higgs."

Yet so far no once has been able to find the Higgs boson in the stream of debris emitted when two particles are smashed together at high speeds. Scientists at another CERN particle collider, LEP, felt they came close before the accelerator shut down in 2000. Scientists using the Tevatron accelerator at Fermilab near Chicago are still hoping to publish a discovery before CERN starts analyzing data later this year. Higgs says he is 90% sure that the LHC will find it, but he doesn't have the final word. "With all respect to our theoretician friends, experiments find out the truth," explains Tejinder Virdee, the head of one of the LHC's experiments. "You can make conjectures, but unless you verify the conjectures, they are metaphysics. That's why many of us haven't minded spending our entire working lives building this experiment."

Higgs jokes that he now tells his doctors to do whatever's necessary to keep him alive until the data from the accelerator can be analyzed. He has his professional reasons for wanting to see his theory confirmed. For the rest of us, solid proof of the Higgs boson would provide a cosmic solace: that beauty and unity exist at the very foundation of the universe, however rare they sometimes seem in the world.

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