Two Parts to the Whole
The project jointly built and managed by Caltech and the Massachusetts Institute of Technology consists of two far-flung parts, each identical in nearly all aspects. One is located here, spread across land carved out of pine forest outside Baton Rouge, La.; the other is splayed on the dry scrub near Hanford, Wash., nearly 2,000 miles (3,000 kilometers) to the northwest.
Each half is made up of a L-shaped arrangement of vacuum pipes, each arm of which is nearly 2.5 miles (4 kilometers) long. Suspended at either end of the pipes are 22-pound (10-kilogram) masses fitted with mirrors. Ultrastable lasers traveling back and forth between the masses a 180-mile (300-kilometer) roundtrip will measure any changes in the distance separating the masses that would indicate the passage of a gravitational wave. Fridays ceremony marked the completion of construction at both sites.
Theory to Experimentation in 83 Years
When the project becomes operational in 2002, it will close a gap between theory and experimentation in the field of gravitational waves that has lagged for nearly a century, said Barry Barish, a Caltech physicist and LIGO director.
Albert Einstein first predicted in 1916 that gravitational waves existed as part of his theory of general relativity; it has taken since then to develop the means to measure them.
"The technology just did not exist to enable the detection of gravitational waves," Barish said.
At the present, physicists dominate the field of gravitational-wave research. Once LIGO becomes operational, however, astronomers will likely embrace it as well.
New Windows on the Universe
Indeed, some expect LIGO will open an entirely new window on the universe, much in the same way the advent of instruments capable of studying other types of radiation, including X-rays and gamma rays, did in past decades.
Gravitational waves, however, are not part of the electromagnetic spectrum, and thus are expected to ferry to Earth information about the universe undetectable by any other means. That could mean when a more sensitive version of the project comes on line within a decade or so, it will be able to detect stirrings in the fabric of space-time as far back the Big Bang and the origin of the universe.
"Gravitational waves, according to general relativity, are so penetrating they should come unscathed by any interaction with matter all the way to us," said Caltech physicist Kip Thorne, who has spent more than three decades working in the field. "Well be able to actually probe the details of the birth of the universe."
LIGO may also herald the discovery of things unimaginable at present.
"It is true we do not know what the final payoff of LIGO will be," said Robert Eisenstein, assistant director of mathematical and physical sciences for the NSF. "It is also true every time we have looked at the universe in new ways there have been incredible surprises."
Thorne said the project could lead to a revolution in our understanding of the universe and the nature of gravity.
Crazy Numbers
The project is no mean feat, however. It must first contend with what Rainer Weiss, a MIT physicist, called a slew of "crazy" numbers.
The changes in distance LIGO must detect are on the order of one one-hundred-millionth the diameter of a hydrogen atom, or 10 to the negative 21st power. That is the equivalent of the width of human hair in the distance between Earth and the closest star beyond our sun.
The mirrors it uses are so flat, were any one blown up to the size of the entire United States, its minute wave-like imperfections would be less than an inch (centimeter) high.
And the instrument is so sensitive, it can be thrown off by the motions in the ground and subsequent changes in its density and thus gravity caused by the tug of a wind-blown trees roots.
"The numbers," Weiss said, "are all crazy numbers."
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