Gravitational waves are distortions or the warping of the very fabric of space-time, which Einstein described as different aspects of reality itself. As a fabric, space-time can be measured either in terms of distance or time.

However, large amounts of mass or energy think here of the incredibly dense core of an exploded star known as a neutron star can curve space-time, resulting in the warping of the fabric which can be observed as gravitational shifts.

When massive objects think now not of one but two neutron stars, each orbiting the other move, the resultant curvature can ripple the space-time fabric, propagating waves outward like those produced by a stone cast into a quiet pond. These waves, however, travel at the speed of light.

Although Einstein first postulated their existence in 1916 as part of his theory of general relativity, gravitational waves have yet to be detected directly.

The best evidence thus far for their existence comes indirectly, courtesy of the work of 1993 Nobel laureates Joseph Taylor and Russell Hulse. The two observed two neutron stars orbiting each other, accelerating as they drew closer together exactly the expected phenomenon if the orbit were losing energy in the form of emitted gravity waves.

The Laser Interferometry Gravitational-wave Observatory project seeks to confirm that those waves in fact exist as its first order of business. But physicists and astronomers expect to soon move beyond that, using the two-part observatory to confirm that black holes also exist and that when they collide, they produce a violent curvature of the space-time fabric.

"What LIGO is designed to do is give us the first opportunity to explore the dark side of the universe," said Caltech physicist Kip Thorne, who has studied gravitational waves for more than 30 years.

Physicists invoke musical metaphors in describing how they will listen to the waves almost piecemeal, or note by note. From those disparate notes, however, they can reconstruct entire musical compositions detailing the waves violent beginning deep in the universe.

"Its a little bit like listening to a symphony," said Barry Barish of Caltech, LIGOs director.

A decade ago, when Caltech and the Massachusetts Institute of Technology first proposed LIGO to the National Science Foundation, there were perhaps just 30 people involved in the study of gravitational waves in the United States. Now, there are at least 10 times as many.