THE MEANING OF GENERAL COVARIANCE OF EINSTEIN THEORY OF GRAVITY

The fundamental symmetry of Einstein's theory of gravity is Lorentz-in variance which leads to a well defined energy-momentum tenser. This is also true for Maxwell's theory of electromagnetism which has an addit ional symmetry clue to its spin one, restmass zero character. Similarl y, the spin two, restmass zero character of the gravitational field le ads to an additional gauge symmetry that happens to be isomorphic to t he concept of general covariance. The gauge-covariant energy-momentum tensor for gravitational interactions vanishes identically.