Mach's principle

Physics.

the proposition that there is no absolute space and that the inertia and acceleration of a body are determined by all of the matter of the universe.

[after E. MACH]

* * *

Hypothesis that the inertial forces acting on a body in accelerated motion are determined by the quantity and distribution of matter in the universe.

Albert Einstein found its suggested connection between geometry and matter helpful in formulating his theory of general relativity; unaware that George Berkeley had proposed similar views in the 18th century, he attributed the idea to Ernst Mach. He abandoned the principle when he realized that inertia is assumed in the geodesic equation of motion (see geodesy) and need not depend on the existence of matter elsewhere in the universe.

* * *

▪ astronomy

      in cosmology, hypothesis that the inertial forces experienced by a body in nonuniform motion are determined by the quantity and distribution of matter in the universe. It was so called by Albert Einstein (Einstein, Albert) after the 19th-century Austrian physicist and philosopher Ernst Mach. Einstein found the hypothesis helpful in formulating his theory of general relativity—i.e., it was suggestive of a connection between geometry and matter—and attributed the idea to Mach, unaware that the English philosopher George Berkeley (Berkeley, George) had proposed similar views during the 1700s. (Berkeley had argued that all motion, both uniform and nonuniform, was relative to the distant stars.) Einstein later abandoned the principle when it was realized that inertia is implicit in the geodesic equation of motion and need not depend on the existence of matter elsewhere in the universe.

* * *