General Theory of Relativity

relativity (rèl´e-tîv¹î-tê), physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference. Space and time are no longer viewed as separate, independent entities but rather as forming a four-dimensional continuum called space-time.

Einstein's general theory of relativity is principally concerned with the large-scale effects of gravitation, unlike the special theory which is mainly applicable in small-scale systems and quantum mechanics. The general theory recognizes the equivalence of gravitational and inertial mass, and asserts that material bodies produce the curvature of the space-time continuum and that the path of a body is determined by this curvature. The theory predicts that a ray of light is deflected by a gravitational field; observations of starlight passing near the sun, first made by Arthur Eddington and colleagues during a 1919 eclipse of the sun, confirmed this. The theory also predicts a red shift of spectral lines of substances in a gravitational field, a result confirmed by observation of light from white dwarf stars. Finally, the theory also accounts for the entire observed perihelion motion of the planet Mercury, only part of which could be explained by Newtonian celestial mechanics. Reconciling the theory with quantum mechanics in a unified field theory has proven difficult. Superstring theory may be able to link quantum gravitation (the study of quantum fields in a curved space-time) with the other quantum theories.