Object-Field Density Equilibrium (OFDE): Dynamic Manifestations of Universal Gravity in Density Fields

Classical physics traditionally interprets gravity as an inherent property of mass or the geometric curvature of spacetime. However, this paradigm faces insurmountable obstacles when addressing singularities, galactic rotation anomalies, and the unification of quantum gravity. This paper proposes the "Object-Field Density Equilibrium" (OFDE) theory to reconstruct the framework of cosmic mechanics from the perspective of fluid dynamics. OFDE posits that cosmic space is permeated by a physical medium field, identified herein as the unification of macroscopic dark matter fluid and microscopic quantum vacuum. Crucially, while affirming that Universal Gravity remains the sole fundamental attractive force, this study argues that in a reality filled with media rather than a perfect vacuum, the final force manifested on an object is not merely attraction, but the net result of a "density equilibrium" between the object and its environment driven by gravity. Specifically, universal gravity causes high static-density objects to undergo "medium sedimentation" (manifesting as downward pull), while forcing low dynamicdensity objects to experience "medium displacement" (manifesting as upward buoyancy). We establish a dynamic density equation incorporating the time dimension and medium coupling terms, proving that velocity dilutes an object’s system density by expanding its "spacetime swept volume." Inertia is redefined as the fluid coupling impedance between matter and the field medium, while orbital motion is identified as the kinematic cost required for objects to maintain a "floating" equilibrium within specific field density layers. This model successfully unifies macro-celestial orbital dynamics with micro-electron quantum stability and reveals the physical nature of black holes as hydrodynamic collapse points where the field medium is punctured by extreme density. Finally, based on the electromagnetic-medium coupling mechanism, this paper presents an engineering concept for "Virtual Volume Expansion" (VVE) and Variable Density Propulsion, providing a theoretical blueprint for propellantless field-dynamic navigation.