Einstein predicted the existence of gravitational waves in 1916, but he later became uncertain and made arguments against their existence. This resulted in the field languishing until the mid-1950’s when theoretical physicists, especially members of the  King’s relativity group  led by Sir Hermann Bondi and Professor Felix Pirani, made significant advances.

In the late 1950’s and early 1960’s Pirani, Bondi, and colleagues, plus students and visitors at King’s, overcame the theoretical obstacles to the existence of gravitational waves in a series of seminal research papers. These demonstrated how general relativity predicted the existence of gravitational waves and the transfer of energy by gravitational radiation. These theoretical advances enabled experimental physicists to start designing detectors to measure if gravitational waves really existed.

The  Laser Interferometer Gravitational-wave Observatory (LIGO)  detectors, operated by Caltech and MIT in the US, have been searching for gravitational waves since 1994. The  LIGO Scientific Collaboration  comprises over 1000 scientists from 17 countries, and includes  Mairi Sakellariadou , Professor of  Theoretical Physics  in the  Department of Physics  at King’s. After a series of upgrades, the LIGO Collaboration announced in February 2016 that they had directly detected gravitational waves for the first time, from two black holes merging – confirming the predictions of the King’s relativity group almost 60 years earlier and Einstein’s predictions from a century ago.

Image copyright: ‘Two Black Holes Merge into One’ CC BY-SA 4.0 Simulating eXtreme Spacetimes (SXS) project (http://www.black-holes.org)