Einstein's theory of relavity, although intriguing as a purely theoretical model, directly challenged many contemporary Newtonian views of his time. His theory gained validity as it predicted various natural phenomena more accurately than former theories. Several important observations and experiments, such as one that utilized the Mössbauer effect to support the existence of a gravitational redshift, put relativity to the test.

Before Einstein's general relativity theory, astronomers could not explain why Mercury, the nearest planet to the sun, revolved in an orbit that was not perfectly elliptical. This phenomenon, referred to as the precession of Mercury’s perhelion (Mercury's perhelion is the point in its orbit during which it is closest to the sun), has puzzled scientists who historically attacked the problem using Newtonian physical laws. Einstein's field equations, which describe the extent of the warping of space-time by massive objects, and his geodesic equations, which describe the path of objects moving through warped space-time, predicted very accurately the seemingly anomalous precession of Mercury's orbit. Because of Mercury's proximity to the sun, it experiences a distortion of its orbit by the significant curvature in space-time caused by the sun.

Not only do Einstein's theorems predict that masses will be affected by curvature of space-time by massive objects, but that even light particles move in curved paths in warped space-time fields generated by massive objects. This prediction was been clearly supported during a partial solar eclipse in 1919. If photons, or light particles, are affected by curved space-time, then we would expect that the light sent from stars would be deflected from its original path by massive objects, such as the sun. However, the bright light cast by the sun made scientific observations of starlight that passed close by the sun extremely difficult. Normally, detection of this starlight is prevented by sunlight, which floods and overpowers the starlight by many degrees of magnitude. During a solar eclipse, when the sun’s light is obscured by the position of the moon, astronomers can avoid this problem. By taking pictures of the blocked sun and the surrounding sky, they can determine whether the position of the starlight is different than it should be in areas where space-time is not warped. Indeed, this hypothesis was confirmed by painstaking observations made in 1919 and during subsequent eclipses. Einstein's general relativity theory again correctly predicted that space-time curved by massive objects would even affect the path of light.