Hundreds of feet beneath the ground outside the Swiss town of Meyrin, near Geneva, a six-year, $660 million construction project is rushing toward a payoff. Workers at the European Center for Particle Physics (CERN) have excavated a 12-ft.-wide circular tunnel that is 16 miles in circumference, installed nearly 5,000 powerful electromagnets, and put along the ring four massive detectors, each weighing several tons but sensitive to the passage of a single subatomic particle. This week, if all goes according to plan, technicians will begin test runs of the largest scientific instrument in the world.
Called the large electron-positron collider (LEP), it...