Correction of an omission in A. Einstein's operational definitions of time and space intervals in the special theory of relativity leads to an improved phenomenological and conceptual foundation for a previously proposed unified field theory. In combination with Einstein's researches on the fluctuation in energy of black body radiation, there results a "new and simple idea" of the kind Professor Richard Feynman felt to be necessary for the solution of the cosmological constant problem. A brief description of the formalism of the theory is presented. The infinite zero-point energy of the vacuum is eliminated. A model for the origin of inertial mass and dark matter-energy is deduced. The resulting relation between observed matter and dark matter-energy leads to a restriction on their magnitudes. The magnitudes of the latter quantities are then estimated from astronomical data. A model is proposed for the origin of the gravitational field in terms of a dynamic process at the basis of the proposed theory. The success of the special theory of relativity in predicting the results of three crucial observations establishing the validity of the general theory of relativity and the elimination of the infinite vacuum energy suggest that the unified field theory can lead to a solution of the cosmological constant problem.