At its introduction in 1915, the
general theory of relativity did not have a solid
empirical foundation. It was known that it correctly accounted for the "anomalous"
precession of the
perihelion of
Mercury and on philosophical grounds it was considered satisfying that it was able to unify
Newton's
law of universal gravitation with
special relativity. That light appeared to bend in gravitational fields in line with the predictions of general relativity was found in 1919 but it was not until a program of precision tests was started in 1959 that the various predictions of general relativity were tested to any further degree of accuracy in the weak gravitational field limit, severely limiting possible deviations from the theory. Beginning in 1974,
Hulse,
Taylor and others have studied the behaviour of
binary pulsars experiencing much stronger gravitational fields than those found in the Solar System. Both in the weak field limit (as in the Solar System) and with the stronger fields present in systems of binary pulsars the predictions of general relativity have been extremely well tested locally.