This work establishes the Spatial Pressure Gravitational Theory (SGT), an original, self-consistent, medium-dynamical theory of gravity, built rigorously from a foundational thought experiment—the Rubber Band Room—which motivates and anchors the entire theoretical framework. From this intuitive physical picture, we derive the nonlinear static field equation of SGT and provide six full mathematical self-consistency tests, unified explanations for nine key observational facts in gravitational phys
