Deep in the pine woods of Livingston Parish, La., physicists are fine-tuning one of the largest and most sensitive scientific instruments, and struggling with the realities of a restless world.

Scientists at the Laser Interferometer Gravitational Wave Observatory (LIGO) are working to filter out the vibrations of passing logging trucks, the night train to New Orleans and the slamming doors down the hallway. If they can, they might soon prove Einstein right and wrong.

Wrong, in that the greatest mind of the 20th century never dreamed that mankind would build a device sensitive enough to detect a passing gravity wave.

Right, because the General Theory of Relativity, published in 1916, proposed the existence of gravity waves. Ripples in the fabric of space-time that LIGO scientists hope to measure for the first time. Theory suggests that gravity waves are formed by some of the most violent events in the universe and are powerful enough to travel unimpeded through anything in their path. Like tachyons, gravity waves may be so subtle that a typical one would distort the Earth by less than the diameter of a single atom. Even though the behavior of many objects can be explained by the existence of gravity waves, they remain one of the few major predictions of Einstein's work not yet confirmed by direct evidence.

LIGO won't produce pictures of faraway places to wow science classes like the $1.6 billion Hubble Space Telescope, another instrument of pure science. LIGO could be even more influential in shaping scientist's view of the universe and the foundations of modern physics.

Newton explained gravity, put forth in his Law of Gravity in 1687, as a force that acts instantaneously over a distance. The same force that acts on an apple falling from a tree or the Earth exerts on the Moon.

Einstein expanded on Newton's view. He perfected a formula for calculating gravitation. Einstein postulated that large objects, such as a planet, will bend the four-dimensional universe in which all things exist. Much the same way someone standing in the middle of a trampoline will "attract" a ball rolling across the surface. Scientists now believe that when objects such as stars collide or explode, they send gravity waves undulating across the space-time continuum like ripples on a pond.

LIGO is a $360 million project funded by the National Science Foundation. It is jointly operated by Cal Tech and MIT and out to catch a passing gravity wave. Then catch another. And another. Sprawling across the flatlands of southern Louisiana, LIGO's arms are more than 2.5 miles long. A weight with a mirrorlike surface is suspended by wires at the end of each of the tunnels. A passing gravity wave is expected to move the mirrors in different directions.

How will they know? They will know by measuring the distance between the mirrors continuously. When fully tuned, lasers sealed in the long vacuum tubes will measure those distances to within one hundred millionth of a single hydrogen atom over the 2.5 mile length. If, for an instant, the distance from the corner station to each mirror is not exactly the same, scientists will be tempted to conclude that a passing gravity wave caused the distortion. If the same distortion occurs simultaneously 2,000 miles away at the LIGO detector in eastern Washington, they will know that they have finally detected a gravity wave, and not some local disturbance. Similar detectors are being built in Germany, Japan and Italy, each eager to be the first to "see" a gravity wave.

So far, the two LIGO installations have completed two warm-up runs, totaling about three months in all. Each data-gathering run was followed by months of refinements. A longer run is scheduled to begin soon. "We are close," says MIT physicist Rainer Weiss, a pioneer in gravity wave research for more than 30 years. "I think sometime in the next two or three years we will see something."

The unprecedented precision required has a high price. "Quiet" is a relative term. Active seismic isolation systems are being added to smooth out the bumps caused by the nearby logging operations. The Hanford, Washington, site has trouble with wind vibrations. Both sites have had to filter out the vibrations from whirring computer fans, humming air conditioners, and distant earthquakes. Waves crashing against the Gulf of Mexico beaches can be seen by the Louisiana LIGO. "No one has done anything like this before, so we didn't know what to expect," says LIGO's Livingston lab director, Michael Zucker. "I'm confident we'll succeed, but it's vastly more complicated than we expected. We've been saying this is a gamble - but one with a very high potential profit."

Humanity's view of the universe was based almost entirely on visible light reaching the Earth until the 1930's. Optical telescopes revealed a largely serene vista of planets, stars and galaxies. The development of radio, infra-red and X-ray telescopes allowed scientists to tap new sources of information (nova). The universe expanded to include brown dwarfs, black holes, quasars and other previously unseen objects. "But even with all of the astronomical instruments we have today, it's estimated that we are seeing only about 4% of the matter in the universe," says LIGO scientist Brian O'Reilly. "That leaves a lot left to discover."

Upgrades are already under design. Even LISA, Laser Interferometer Space Antenna, a three satellite version of LIGO.

Source: Mike Toner, Atlanta Journal-Constitution, 9/14/2003, pg. D1 and 4