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Gravity Waves Elude First Scrutiny

DENVER--The physicists of the Laser Interferometer Gravitational-Wave Observatory (LIGO) are searching desperately for signs that the globe is being squashed by an interstellar traveler. They're looking for the telltale stretch-and-squish signature of gravitational waves distorting the fabric of spacetime--and Earth along with it. Today at the meeting here of the American Association for the Advancement of Science (ScienceNOW's publisher), scientists presented the first results from LIGO: They have no sign yet of gravitational waves.

The $365 million twin observatories--based in Washington and Louisiana--beam lasers down 4-kilometer-long tubes to detect a tiny warping of space associated with the passing of a gravitational wave, a phenomenon predicted by Einstein's general theory of relativity. The lasers are at right angles to each other; a gravitational wave would likely shrink one and stretch the other, causing a faint flicker when the beams are brought together.

So far, no gravitational waves have shown up in any of the projects' first four experiments. The analyses concern different types of gravitational waves. The LIGO interferometers searched for a sudden burst of waves caused by the collapse of a dying star, for example, as well as for the increasingly high-frequency chirp of two massive stars spiraling into each other. Two other searches, for periodic sources analogous to electromagnetic pulsars and for a rumbling background of gravity waves left over from the very early age of the universe, also came up short.

Since it began operating in October 2000, LIGO scientists have been struggling to reduce the amount of noise--such as the low murmur of seismic vibrations and the earth-rattling whine of loggers' saws in Louisiana--that shake the machine and prevent it from seeing the subtle signals of gravity waves (Science, 16 August 2002, p. 1115). According to LIGO team member Rainer Weiss, a physicist at the Massachusetts Institute of Technology, these problems should be coming to an end soon. "Now, at the sweet spot, we're a factor of 10 away from our design sensitivity. Though we're not there yet, we're within shooting distance," he says.

Related site
LIGO's home page