Mass Field Momentum Coupling Theory: Unified Dynamical Framework and Interpretation of Gravitational Phenomena

Based on classical field theory and the differential rules of multivariate functions, this paper takes mass as a four-dimensional spacetime scalar field. Starting from the basic definition of momentum change rate, a unified dynamical theory of mass field coupled with motion is established. The universal expression of the additional force driven by mass field variation is derived as follows: Under the steady-state field condition, it can be simplified to: The necessary and sufficient conditions for this force are the inhomogeneous spatial distribution of mass and the motion of objects. The theory can uniformly explain gravitational phenomena and provide a new field-theoretical approach for the unification of interactions. This paper constructs the basic theoretical system, gives core definitions, axioms, derivations and application prospects, and provides a unified framework for further research.