It is widely supposed that the true test of a theory is in the comparison of its predictions with the results of experiment. Yet, with the benefit of hindsight, one can say today that Einstein’s successful explanation in 1915 of the previously measured anomaly in Mercury’s orbit was a far more solid test of general relativity than the verification of his calculation of the deflection of light by the sun in observations of the eclipse of 1919 or in later eclipses. That is, in the case of general relativity a retrodiction, the calculation of the already-known anomalous motion of Mercury, in fact
...more
