We present Structural Differentiation Gravity (SDG) v2.1, a minimal and falsifiable structural framework for gravitational dynamics, extending to rotational and strong-gravity regimes. Instead of interpreting gravity as spacetime curvature sourced by mass-energy, SDG describes gravity as the observable manifestation of structural differentiation within a closed relational system. The theory is defined by a single minimal equation: g = -α∇C + β(∇ × Γ) where C is structural density and Γ is a structural connection field encoding directional relational organization. This formulation corresponds to a Helmholtz-type decomposition of the effective gravitational field, separating attraction (gradient) and rotation (vorticity). A key feature of SDG is that rotational phenomena—such as frame-dragging and Kerr-like effects—emerge from structural vorticity rather than spacetime geometry. Black holes are reinterpreted as saturation states of structural differentiation, eliminating the need for singularities. Importantly, SDG introduces no new fields or particles. Instead, it provides a structural reinterpretation of known gravitational phenomena. The framework yields observationally distinguishable predictions, particularly in rotational signatures and strong-gravity regimes. This work provides a concrete observational criterion: If rotation is geometric → SDG fails If rotation is structural → SDG survives This establishes SDG as a testable alternative to geometric gravity.
Koji Okino (Fri,) studied this question.