Final answer:
Einstein produced his theory on gravitational waves in 1916, within his general theory of relativity. Direct evidence supporting this theory came in September 2015 when LIGO detected waves from a black hole merger, confirming Einstein's predictions.
Step-by-step explanation:
Albert Einstein produced a theory about gravitational waves in 1916 as part of his general theory of relativity. This theory revolutionized our understanding by describing gravity as the warping of spacetime by mass. Gravitational waves are ripples in spacetime that propagate outward at the speed of light, generated by massive accelerating objects, such as the merger of black holes.
The first indirect evidence for gravitational waves came from the observation of a binary pulsar by astronomers in 1974, and then in September 2015, direct detection by LIGO confirmed Einstein's predictions. Observations of black hole mergers through gravitational waves not only opened a new window into the universe but also provided rigorous tests of general relativity's predictions in strong gravitational fields, which matched remarkably well with the observed data.