equivalence principle

Physics.

(in relativity) the principle that, in any small region of space-time, the effects of a gravitational field are indistinguishable from those of an appropriate acceleration of the frame of reference. Also called Einstein's equivalency principle, principle of equivalence.

[1915-20]

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Fundamental principle of physics that in its weak form states that gravitational (see gravitation) and inertial (see inertia) masses are the same.

Albert Einstein's stronger version states that gravitation and acceleration are indistinguishable. It implies that the effect of gravity is removed in a suitably accelerated reference frame, such as an elevator with its cable cut, in which a person would experience free fall.

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▪ physics

      fundamental law of physics that states that gravitational (gravitation) and inertial forces are of a similar nature and often indistinguishable. In the Newtonian form it asserts, in effect, that, within a windowless laboratory freely falling in a uniform gravitational field, experimenters would be unaware that the laboratory is in a state of nonuniform motion. All dynamical experiments yield the same results as obtained in an inertial state of uniform motion unaffected by gravity. This was confirmed to a high degree of precision by an experiment conducted by the Hungarian physicist Roland Eötvös (Eötvös, Roland, Baron von). In Einstein's version, the principle asserts that in free-fall the effect of gravity is totally abolished in all possible experiments and general relativity reduces to special relativity, as in the inertial state.

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