Unified Formalism of Four Fundamental Interactions Based on the Space-Substance Medium Model

The unification of the four fundamental interactions remains one of the cen tral pursuits in theoretical physics. While the Standard Model of particle physics provides a unified description of the strong, weak, and electromagnetic interac tions, a self-consistent integration with gravitation has not yet been achieved. This work proposes an alternative theoretical framework based on the space-substance medium hypothesis, which postulates that all interactions originate from the ab sorption and perturbation of the space-substance background by matter, and differ entiate into four fundamental interaction types through distinct modulation mech anisms. Within this framework, we derive a unified master formula for interactions, and present the full velocity-compatible expressions for gravitation, strong interaction, electromagnetic interaction, and weak interaction, together with their low-speed degenerate forms. Key phenomenological parameters, such as the nucleon direc tional enhancement coefficient, are calibrated against well-established experimental data. The consistency of the formulas with classical physics and special relativ ity under low-speed and weak-field conditions is verified. We also establish the conversion relation between the equivalent dynamical mass of high-speed particles and the absolute rest mass, clarify the physical differences between this model and the relativistic mass concept, and provide a standardized calculation procedure together with applicability boundary criteria. This work provides a new exploratory path for the unified description of funda mental interactions, whose strong-field and high-energy predictions remain to be further tested experimentally.