Research on the Nature of Gravitational Field and the Common Laws of the Fundamental Interactions on the Basis of "Expanding Balloon" Model

The fundamental nature of gravitational fields and the common laws governing the four fundamental interactions remain among the most cutting-edge research challenges in physics. To address these two major scientific problems, this paper establishes a physical model of a gravitational field on the basis of an "expanding balloon" analogy. Through the study of this single model, it is deduced that a gravitational field is a form of massless, intangible, spherical field substance that extends uniformly and infinitely outward at the speed of light from the center of mass of an object with mass. This model also elucidates the physical mechanism underlying the equivalence of the gravitational mass and inertial mass. Furthermore, by simulating and analyzing a dual-model framework, the study derives key conclusions regarding the physical mechanism of gravity, the conditions for its generation, the mediator of gravitational interaction, the speed of gravitational propagation, and the mathematical formulation of the gravitational mechanism. Given that all four fundamental interactions arise from field-field interactions, further investigation not only yields mathematical expressions for the electromagnetic, strong, and weak forces but also reveals five universal laws governing all four fundamental forces: the zero-distance contact principle, the inverse-square law, the Yan Zijie's middle principle, the field divergence principle, and the field mutual noninterference principle. These principles are described using mathematical formulations.