WHY THE ENERGY OF THE GRAVITATIONAL-FIELD CAN BE LOCALIZED

The tetrad formalism of general relativity, in Scherrer's version, all ows one to localize the gravitational energy-momentum (GEM) in a simpl e and ''natural'' way, with the exclusive help of physically well-foun ded arguments. (This theory does not contain any ad hoc hypotheses, su ch as more or less disputable coordinate conditions or an arbitrary fi xing of the gauge.) The theory is structured as follows: (1) local ene rgy-momentum conservation laws allow one to define a tensor GEM densit y; (2) definition of a gravitational 4-force density, which implies a tensor representation of the gravitational field (in contrast with the nontensorial Gamma(mu nu)(lambda) of Einstein's formalism); (3) thank s to this representation, we prove that the equivalence principle is n ot inconsistent with the GEM localizability concept; (4) physically we ll-justified supplementary conditions for the tetrads are proposed ('' alignment'' of the tetrads); (5) an example is discussed in detail, in connection with the symmetry properties of the GEM tensor.