General relativity is a very successful theory of gravity; so far no discrepancies with experiment are known. Yet at a fundamental level the theory is incomplete, since it does not include quantum effects. Modern attempts to make a quantum description of gravity predict small deviations from the predictions of general relativity. The detection of gravitational waves from colliding black holes has opened up new possibilities for finally testing general relativity in the strong-field regime.
In a Department of Physics Colloquium on March 27, 2018, part of the Bethe Lecture Series, Saul Teukolsky describes how LIGO is already able to perform interesting tests and discusses the future of such tests, both with ground-based and space-based detectors. Teukolsky is the Hans A. Bethe Professor of Physics and Astrophysics.