The Equivalence Principle, the Covariance Principle
and
the Question of Self-Consistency in General Relativity
C. Y. Lo
Applied and Pure Research Institute
17 Newcastle Drive, Nashua, NH 03060, USA
September 2001


Abstract
The equivalence principle, which states the local equivalence between acceleration and gravity, requires that a free falling observer must result in a co-moving local Minkowski space. On the other hand, covariance principle assumes any Gaussian system to be valid as a space-time coordinate system. Given the mathematical existence of the co-moving local Minkowski space along a time-like geodesic in a Lorentz manifold, a crucial question for a satisfaction of the equivalence principle is whether the geodesic represents a physical free fall. For instance, a geodesic of a non-constant metric is unphysical if the acceleration on a resting observer does not exist. This analysis is modeled after Einstein£r illustration of the equivalence principle with the calculation of light bending. To justify his calculation rigorously, it is necessary to derive the Maxwell-Newton Approximation with physical principles that lead to general relativity. It is shown, as expected, that the Galilean transformation is incompatible with the equivalence principle. Thus, general mathematical covariance must be restricted by physical requirements. Moreover, it is shown through an example that a Lorentz manifold may not necessarily be diffeomorphic to a physical space-time. Also observation supports that a spacetime coordinate system has meaning in physics. On the other hand, Pauli£r version leads to the incorrect speculation that in general relativity space-time coordinates have no physical meaning
1. Introduction.
Currently, a major problem in general relativity is that any Riemannian geometry with the proper metric signature would be accepted as a valid solution of Einstein£r equation of 1915, and many unphysical solutions were accepted [1]. This is, in part, due to the fact that the nature of the source term has been obscure since the beginning [2,3]. Moreover, the mathematical existence of a solution is often not accompanied with understanding in terms of physics [1,4,5]. Consequently, the adequacy of a source term, for a given physical situation, is often not clear [6-9]. Pauli [10] considered that ¥Phe theory of relativity to be an example showing how a fundamental scientific discovery, sometimes even against the resistance of its creator, gives birth to further fruitful developments, following its own autonomous course." Thus, in spite of observational confirmations of Einstein£r predictions, one should examine whether theoretical self-consistency is satisfied. To this end, one may first examine the consistency among physical ¥Lrinciples" which lead to general relativity.
The foundation of general relativity consists of a) the covariance principle, b) the equivalence principle, and c) the field equation whose source term is subjected to modification [3,7,8]. Einstein£r equivalence principle is the most crucial for general relativity [10-13]. In this paper, the consistency between the equivalence principle and the covariance principle will be examined theoretically, in particular through examples. Moreover, the consistency between the equivalence principle and Einstein£r field equation of 1915 is also discussed.

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