The latest detector to join the hunt for gravitational waves is the €76 million ($86 million) Virgo, an Italian-French collaboration near Pisa that celebrated its inauguration and started testing at the end of July. “The curious thing is, these detectors do classical physics experiments, yet—as a network—they can get quantum mechanical information about the graviton’s spin,” says Barry Barish, director of the Laser Interferometer Gravitational Wave Observatory (LIGO), a similar US project (see the article by Barish and Rainer Weiss in Physics Today, October 1999, page 44).
Virgo, like LIGO, is a Michelson–Morley interferometer. Virgo’s two perpendicular arms are each three kilometers long; LIGO’s two interferometers have arms four kilometers long. A laser beam is split and sent down both arms, reflected, and later recombined. An impinging gravitational wave would, by nudging the end mirrors outward and inward, stretch one arm and squeeze the other. The difference in...
