At two remote locations in the United States—one set amid marshes and cypress stands near Livingston, Louisiana, and the other on the arid, treeless plains outside of Richland, Washington—teams of scientists in 2001 were tuning up the largest and most sensitive measuring devices ever built. The instruments were components of the Laser Interferometer Gravitational-Wave Observatory (LIGO), which was designed to observe a natural phenomenon called "gravity waves," predicted by the renowned German-born physicist Albert Einstein in 1916.

Much as waves of water can form ripples on the surface of a quiet pond, gravity waves are ripples in the fabric of space and time. Most scientists in 2001 were convinced that gravity waves exist, despite the fact that none had ever been directly detected. In 1993, two Americans, Russell Hulse and Joseph Taylor, were awarded the Nobel Prize in physics for discovering convincing indirect evidence of the presence of gravity waves. For many scientists, this evidence and the challenge of discovering and studying gravity waves were strong enough to lure them to the remote outposts of LIGO.

LIGO (pronounced LIE go) is a joint effort of the Massachusetts Institute of Technology (MIT) and the California Institute of Technology (Caltech). The National Science Foundation (NSF), an independent U.S.-government agency responsible for promoting science and engineering, provided about $300 million to build LIGO, the largest project ever funded by the agency.

However, LIGO was not alone in the hunt for proof of gravity waves. In 2001, several other gravity-wave observatories were in operation, under construction, or in the planning stages. TAMA, an instrument similar to but smaller than LIGO, was operating near Tokyo. Virgo, a joint French-Italian project, was under construction near Pisa, Italy. And a third observatory, called GEO, was to be built near Hanover, Germany.