Einstein’s centennial gift: Gravitational waves discovered

Sanjeev Dhurandhar and Sanjit Mitra

Inter University Centre for Astronomy & Astrophysics, Ganeshkhind, Pune 411 007, India.

A spectacular prediction of Einstein’s general theory of relativity is gravitational waves. A century ago - in 1916 - Einstein predicted the existence of gravitational waves. Gravitational waves have now been detected by the LIGO detectors in the US. The physical existence of the waves was established long before by the observations of the Hulse-Taylor binary pulsar whose orbit decays exactly as predicted by Einstein’s general theory of relativity. Weakness of the gravitational force implies that the waves are extremely difficult to detect - one must effectively measure distances much smaller than the size of a proton. During the past half century, technology has taken immense strides and the current advanced detectors are now capable of reaching the requisite sensitivity to detect the waves. Gravitational waves carry information about their dramatic origins and about the nature of gravity that cannot be otherwise obtained. A new astronomical window to the universe has been opened. This article will describe the physics of gravitational waves, the technological feats necessary for the detector to achieve unprecedented sensitivities, the current and future global efforts in this direction, the gravitational wave event that was detected, the Indian initiative and contribution to the global effort and the astrophysics that we can learn from this.