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The Advocate News LIGO-G020290-00-L Monday, July 15, 2002
LIVINGSTON -- The Laser Date: Mon, 15 Jul 2002
14:01:28 -0700 (PDT) On Aug. 23, the "L" -shaped observatory nestled in the woodlands of Livingston Parish is scheduled to begin searching for gravitational waves. The goal: unlocking some of the deepest secrets of the universe. For several years, engineers, scientists and technicians have been working to build a huge facility; they designed, created and installed equipment to fill it and then tuned those pieces of equipment to work as a precision unit. That "slow, methodical" tuning has resulted in "getting devices to work together optimally," said California Institute of Technology's Mark Coles, director of the Livingston facility. Scientists, engineers and technicians from Cal Tech, the Massachusetts
Institute of Technology and other universities have tested pieces of
equipment individually and as part of subsystems. Eight times they have
linked the equipment for engineering runs.
Now LIGO will look for the world's first recording of a gravitational wave, which could be caused by any of a number of cataclysmic events in the universe. "We've achieved a sensitivity that we feel can make a statement that isn't trivial," Coles said. "It's an exciting time," said LSU's Warren Johnson, who'll be involved in the first science run. Johnson, a pioneer in the attempt to find gravitational waves, says LIGO is far more sophisticated than the aluminum bars he and other scientists once hoped to get to "ring like a bell" if a gravity wave of the right frequency passed through them. LIGO will be able to look at a much broader spectrum of waves, he said. At LIGO, scientists will split a laser beam, run the two beams through two-and-a-half-mile vacuum tunnels and bounce them off specially made mirrors. Theoretically, a gravitational wave will cause a ripple in the fabric of space and time. That ripple, Coles said, should cause the distance in one arm of the "L"- shaped structure to expand while the other contracts. The change in distance -- estimated to be one-hundred-millionth the diameter of a hydrogen atom over the four-kilometer length of each arm -- should throw the separated laser beams out of phase, according to LIGO physicists. Don't expect immediate announcements of the discovery of a gravitational wave, however. Even if one should show up in the first science run, scientists will have a lot of work to do on the raw data produced. They'll have to sift through the earthly vibrations recorded on the instruments. That will include activity on Interstate 12 and maybe even a tree falling in the nearby forest. In their search, they're armed with theories on what a gravitational wave should look like. Anything that appears to be a gravitational wave will also have to appear at the same time at Livingston's sister facility in Hanford, Wash. Otherwise, scientists will assume it was local -- not celestial -- in origin. An ideal situation would involve recording gravitational waves at the two sites in conjunction with a conventional observation of the astronomical event that caused it. Physicist Albert Einstein postulated the existence of gravitational waves in his 1916 general theory of relativity, but physicists aren't sure how often gravitational waves hit the earth or that the present version of LIGO is sensitive enough to record them. Coles said a future re-tooling of LIGO will make the huge instrument far more sensitive, particularly in the low frequencies, which physicists believe to be "richer" in gravity waves. Among other things, the next version of LIGO will probably include sapphire mirrors being researched by Southern University's Stephen C. McGuire. That research is progressing and promises the broader benefit of better understanding sapphire and other materials being scrutinized, McGuire said. Scientists say the same holds true for the high-quality laser designed for LIGO, as well as cutting-edge optics, vacuum technology and measurement science developed for the facility. Among a number of things LSU scientists are doing in connection with LIGO, some are working on more sophisticated means of isolating the mirrors from the "noise" of movement on the earth and even by the earth, Coles said. Seismic and even tidal forces can cause noise in the sophisticated
mechanism, he said.
Although a LIGO upgrade is planned, that doesn't mean the current instrument won't find gravitational waves, said LSU physicist Ed Daw, who is doing post-doctoral work at LIGO. "LIGO 1 has a good chance of seeing surprises," he said. "The sensitivity is better than anything used before" in the search for gravitational waves. Even if the current version of LIGO finds nothing within the range of frequencies it can monitor, that will be important scientific information, Daw said. If the twin facilities do detect something, "then we have to start doing our homework," he added. Physicists are interested in more than just proving the existence of gravitation waves, Coles said. For one thing, astronomers and physicists hope to determine the sources of individual waves. Absent a conventional sighting, they would use triangulation with the facility in Washington and one of the interferometers recently built by other groups in Europe and Japan. More importantly, the waves should contain information that provides a better understanding of the physical make-up of the universe, Coles said. He compared gravitation-wave sensors to radio telescopes, which gave scientists radio waves to study in addition to the light astronomers have long studied from optical telescopes. With radio telescopes came a new understanding of celestial mechanics. Coles said gravitation waves also should provide a new window of information. Scientists will be looking for data on things like the structure of black holes, the cores of supernovae and what happens when a pair of neutron stars merge. "We hope to learn something about matter in its most extreme form -- when entire stars are compressed into the density of an atomic nucleus," Johnson said. But Coles said scientists don't know what else they might find, since most of the calculated matter of space remains dark to the instruments scientists have used until now. "Big surprises are likely," said physicist Kip Thorne. The Cal Tech Feynman Professor of Theoretical Physics described LIGO as
"a tool for exploring the unknown." |
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