Signals From Distant Disasters

By MICHAEL D. LEMONICK

When Albert Einstein unveiled his general theory of relativity in 1916, he predicted several phenomena that could be used to test its validity. Two of them -- that light is bent by gravity and that the orbit of Mercury wobbles in a certain way -- were confirmed within just a few years, convincing scientists that relativity was a revolutionary discovery, not just a mathematical curiosity. But Einstein thought another of his claims would never be proved. His theory predicted that fast-moving, massive objects emit gravity waves, small distortions moving through the fabric of space and time. Einstein said these waves would be virtually undetectable, and it was not until a few years ago that physicists began their so far futile search for the elusive ripples.

Now scientists are suddenly optimistic about finding this missing link in Einstein's theory. A new facility called the Laser Interferometer Gravitational-Wave Observatory (LIGO), planned for completion in 1995, could provide the first direct evidence that gravity waves exist. The $192 million project recently got a thumbs-up from President George Bush, who asked Congress for $47 million in start-up funding as part of his proposed 1991 budget. The search for a suitable site has already begun.

LIGO will be 100 to 1,000 times as sensitive as existing gravity-wave detectors. That should be enough not only to confirm relativity but also to probe deeply into the most violent processes in the cosmos, including ) exploding supernovas, collisions between black holes, and "starquakes" on the semisolid surfaces of neutron stars. All of these phenomena are believed to send out characteristic bursts of gravity waves. Says Rochus Vogt, the Caltech physics professor who heads the joint M.I.T.-Caltech team that will build LIGO: "We are going to look at a whole new force as a transmitter of signals from the universe. That is bound to bring big surprises."

LIGO will measure the minute motions of hanging weights as they ride the waves. The observatory will not be a single facility but a pair of installations separated by at least 1,600 km (1,000 miles) to rule out false signals from, say, local earthquakes. Each L-shaped installation will consist of two pipes 4 km (2.5 miles) long, set at right angles to each other and emptied of air. A laser, placed at the intersection of the pipes, will emit a beam that is split into two parts, each of which will bounce back and forth between suspended weights and finally return to the intersection. There the beams will be recombined, and a detector will examine them for slight distortions that will reveal whether movements of the weights have forced one light beam to travel as little as one ten-quadrillionth of a centimeter farther than the other, a likely signal that gravity waves have affected them.

While the two LIGO installations by themselves will enable scientists to tune in to heavenly disasters, the addition of two more facilities would make it possible to determine the precise locations of the events. Says Vogt: "There are proposals pending to build gravity-wave observatories in Europe and Australia, and we're hoping to put together an international network." That will take time, and some of the most important discoveries lie years in the future. But just as Galileo did with his crude telescope in the early 1600s, the first generation of gravity-wave astronomers will undoubtedly learn things right away that will dramatically enrich science's understanding of the universe.

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CREDIT: TIME Diagram by Joe Lertola

CAPTION: CATCHING A WAVE