Chapter

The principle of equivalence

Ta-Pei Cheng

in Relativity, Gravitation and Cosmology

Second edition

Published in print November 2009 | ISBN: 9780199573639
Published online February 2010 | e-ISBN: 9780191722448 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199573639.003.0004

Series: Oxford Master Series in Physics

                      The principle of equivalence

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After a review of the Newtonian theory of gravitation in terms of its potential function, we start the study of general relativity (GR) with the introduction of the equivalence principle (EP). The Weak EP (the equality of the gravitational and inertial masses) is extended by Einstein to the Strong EP, the equivalence between inertia and gravitation for all interactions. This implies the existence of “local inertial frames” at every spacetime point. In a sufficiently small region, the “local inertial observer” will not sense any gravity effect. The equivalence of acceleration and gravity means that GR (physics laws valid in all coordinate systems, including accelerating frames) must necessarily be a theory of gravitation. The strong EP is used to deduce the results of gravitational redshift and time dilation, as well as gravitational bending of a light ray.

Keywords: Newtonian theory of gravitation; equivalence principle; weak vs strong EP; gravitational mass; inertial mass; gravitational redshift and time dilation; bending of light ray

Chapter.  9440 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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