There is little doubt that gravitational waves exist. Indirect evidence for them is compelling. But astrophysicists are keen to observe them directly for the information they can provide, and despite the efforts of teams of researchers working at extraordinarily sensitive interferometers (see, for example, the article by Barry Barish and Rainer Weiss in PHYSICS TODAY, October 1999, page 44), direct observation has yet to happen. The null result is not entirely unexpected. As sensitive as the current interferometers are, gravity is so weak that it would take a rare event, such as the merging of two black holes fairly close to Earth, to produce a wave strong enough to detect. Such events come along at most once every several years.
Any further increase in the interferometers’ sensitivity would pay off rapidly. Reducing the noise by a factor of x increases the volume of space from which an event can...
