Mach's principle (mäks) [for E. Mach Mach, Ernst (ĕrnst mäkh), 1838–1916, Austrian physicist and philosopher, b. Moravia.
..... Click the link for more information. ], assertion that the inertial effects of mass mass, in physics, the quantity of matter in a body regardless of its volume or of any forces acting on it. The term should not be confused with weight , which is the measure of the force of gravity (see gravitation ) acting on a body.
..... Click the link for more information. are not innate in a body, but arise from its relation to the totality of all other masses, i.e., to the universe as a whole. Thus, the inertial forces experienced by a body in accelerated motion have the same physical origin as the gravitational forces it experiences near mass concentrations, namely the mass-energy field field, in physics, region throughout which a force may be exerted; examples are the gravitational, electric, and magnetic fields that surround, respectively, masses, electric charges, and magnets. The field concept was developed by M.
..... Click the link for more information. described by the general theory of relativity relativity, 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.
..... Click the link for more information. . Inertial forces have a much longer range than gravitational forces, so the role of very distant matter becomes preponderant. According to Mach's principle, a body experiences no inertial forces when it is at rest or in uniform motion with respect to the center of mass center of mass, the point at which all the mass of a body may be considered to be concentrated in analyzing its motion. The center of mass of a sphere of uniform density coincides with the center of the sphere.
..... Click the link for more information. of the entire universe. When its motion is nonuniform (accelerated) with respect to the total mass of the universe, it experiences forces such as centrifugal force (see centripetal force and centrifugal force centripetal force and centrifugal force, action-reaction force pair associated with circular motion .
..... Click the link for more information. ) and the Coriolis effect Coriolis effect (kôr'ē-ō`lĭs) [for G.-G.
..... Click the link for more information. . Hence, the "local" behavior of matter is influenced by the "global" properties of the universe, i.e., those properties that describe the universe as a whole, which are studied in cosmology cosmology, area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe .

Modern Cosmological Theories

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Mach's principle

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.