Giorgio Gratta, a physicist at Stanford University, is going fishing for high-energy neutrinos, ghostly subatomic particles that bombard Earth from unknown objects in deep space. These particles can interact with water, emitting a shudder of light, albeit under such rare circumstances that just a few of them strike each square mile of ocean each year. But neutrinos can also heat the water, generating acoustic waves. The Navy's Atlantic Undersea Test and Evaluation Center, a 100-square-mile hydrophone array used to track ships and weapons during undersea naval exercises, could pick up these tiny vibrations. "You can put hydrophones in the water and listen to the neutrinos," Gratta says.
During the past several months, Gratta and his students have begun collecting data from seven of the array's 52 hydrophones. He is using computer software to filter out noise from wind, surf, ship engines, snapping shrimp, and echolocating dolphins. "Things look good," he says. Next he hopes to plug into the rest of the hydrophones, start tallying the neutrinos, and begin to zero in on the strange, energetic objects that emit them.