Stephen Hawking did not predict the existence of gravitational waves before they were discovered by the Laser Interferometer Gravitational-Wave Observatory (LIGO) experimenters. Gravitational waves were first predicted by Albert Einstein in 1916 as a consequence of his theory of general relativity. However, it took several decades for experimental technology to advance enough to detect these waves directly.
Stephen Hawking made significant contributions to the field of theoretical physics, particularly in the study of black holes and the nature of the universe. He conducted extensive research on various aspects of black holes and their behavior, including their emission of radiation (Hawking radiation). However, his work did not involve predicting the detection of gravitational waves.
The discovery of gravitational waves by LIGO was announced in February 2016, and it was a monumental achievement in the field of astrophysics. The detection confirmed the existence of gravitational waves and provided direct evidence supporting Einstein's theory of general relativity.