Physical Reconstruction of the Essence of Gravity — Gravity Generation Mechanism via Flux Conservation of the Cosmic Inertial Spacetime Field and Inertial Constraint Reaction Force

Traditional gravitational theories suffer from fundamental defects such as action-at-a-distance and difficulty in unification. Based on Galileo’s law of inertia, this paper proposes the inertial space-time field theory, redefining gravity as the reaction force generated when an object moves inward within the inertial space-time field and is constrained by the surface of a celestial body. The core mechanism is as follows: the high-density inertial space-time field inside a celestial body drives matter to move inward and compact it, forming a compacted layer; the Sun’s rotation drags the external space-time field through a coupling-decoupling mechanism, producing a hierarchical rotation with faster inner and slower outer regions, explaining the spiral structure of galaxies, the elastic precession of planets, and the perihelion precession. Theoretical elevation: the subject of inertial motion is the space-time field itself, and material motion is determined by the field distribution, achieving a grand unification of inertial motion, orbital motion, and falling motion.The internal and external fields couple at the boundary of the constraint layer, and the system possesses the intrinsic property of tending toward equilibrium with high-density regions. The lunar shielding effect naturally explains the bimodal tidal pattern. The combined action of solar rotational dragging and field constraint explains the coplanar thin-disk structure of the solar system and galactic disks.Taking the perihelion precession of inner planets as the research object, this paper derives the formulas using only the space-time field flux Φ as the fundamental physical quantity, without introducing the speed of light c, the gravitational constant , or the central mass . The theoretical values are in excellent agreement with observational data. Simultaneously, the flux is independently calculated based on the Earth's measured gravitational acceleration and radius, showing high consistency with results from the Newtonian framework. This model requires no assumptions of gravitational mass, dark matter, or space-time curvature, achieving a unified classical mechanical description from terrestrial gravity to galactic morphology.