ar X iv : g r - qc / 9 60 50 27 v 1 1 5 M ay 1 99 6 Workshop on Gravitational Waves ∗ Bala

According to general relativity any change in the gravitational field of a compact gravitating system like neutron star or black hole, will produce a ripple on the spacetime which will propagate with the speed of light. This is a gravitational wave. Although gravitational waves have been predicted from the very early days of general relativity they have not yet been detected directly. Nevertheless, their indirect influence on the evolution of compact binary systems has been observed almost 20 years ago, and the observational results agree to remarkable accuracy with the theoretical predictions. Almost thirty five years ago attempts were made to detect these tiny ripples in the spacetime by constructing gravitational wave detectors in the form of resonant bars. Today these detectors are either narrowband resonant bars or spheres or broadband laser interferometers. The resonant detectors are already in operation and they have achieved sensitivities close to their limits, while the laser interferometers (LIGO, VIRGO, GEO600) are in the construction phase and expected to become operational before the end of this century. The next generation of gravitational wave detectors includes space experiments like LISA accepted by ESA as a possible cornerstone mission. The direct detection of the gravitational waves will not only be a great triumph for Einstein’s theory of relativity but is expected to signal a new era in astronomy by opening a non electromagnetic window of observation. By a network of at least three laser interferometers one