Gravitational waves are ripples in the fabric of space and time produced by violent events in the distant universe, for example by the collision of two black holes or by the cores of supernova explosions. Gravitational waves are emitted by accelerating masses much as electromagnetic waves are produced by accelerating charges. These ripples in the space-time fabric travel to Earth, bringing with them information about their violent origins and about the nature of gravity.

Albert Einstein predicted the existence of these gravitational waves in 1916 in his general theory of relativity, but only now, in the 1990s, has technology become powerful enough to permit detecting them and harnessing them for science. Although they have not yet been detected directly, the influence of gravitational waves on a binary pulsar (two neutron stars orbiting each other) has been measured accurately and is in good agreement with the predictions. Scientists therefore have great confidence that gravitational waves exist. Joseph Taylor and Russel Hulse were awarded the 1993 Nobel Prize in Physics for their discovery of this binary pulsar.

The data challenge of LIGO stems from the very small expected size of the signal in comparison to noise sources (seismic, acoustic, electrical, and many others), and from the great rarity of the events to be detected (less than one per year). Many other data channels must be monitored in addition to the gravity-wave instrument itself, and their effects carefully subtracted. Large amounts of peripheral data must be stored, since the confirmation of a candidate inspiral event will demand very close examination.