Momentum Coherence as the Origin of Galaxy Rotation Curves: Empirical Validation and Transition Radius Prediction from SPARC

Galaxy rotation curves remain one of the central observational challenges in astrophysics, traditionally motivating the introduction of non-baryonic dark matter components. In this work, we present an alternative explanation based on large-scale kinematic coherence, formulated within the MIND (Momentum in Inertial / Non-Inertial Dynamics) framework. We show that when stellar orbits exhibit coherent angular momentum over galactic scales, an additional kinematic contribution naturally emerges, leading to an effective modification of the observed circular velocity profile. This contribution is expressed through a simple and testable relation, V²(R) = V²_Newton(R) + (ΩR)², where Ω characterizes the global coherence of the system. Using high-quality SPARC galaxy data, we demonstrate that this formulation reproduces observed rotation curves and enables predictive estimates of characteristic galactic radii without invoking dark matter halos. A dedicated methodological analysis is presented, introducing a residual-based approach that cleanly separates Newtonian baryonic dynamics from the coherent momentum term, ensuring robust parameter inference even when the latter is subdominant. Extensive robustness tests using controlled synthetic stellar populations show that the coherence parameter Ω can be accurately recovered under realistic observational noise, significant baryonic mass uncertainties, and varying sample sizes. The method exhibits the expected statistical scaling and remains stable across a wide range of astrophysical conditions. The results establish kinematic coherence as a viable and falsifiable physical mechanism underlying flat galaxy rotation curves, and provide a clear pathway for direct application to Gaia DR3 stellar kinematics. We present an empirical validation of the Momentum in Inertial/Non-Inertial Dynamics (MIND) framework using 135 rotation-supported galaxies from the SPARC database, comprising 3014 independent radial data points. MIND demonstrates that the observed departure from Newtonian expectations emerges from a universal threshold in organized momentum density, through a saturable coherence response of spacetime. We show that MIND reproduces the Radial Acceleration Relation (RAR) with statistical performance comparable to Modified Newtonian Dynamics (MOND), achieving an RMS scatter of 0.451 dex versus 0.377 dex for MOND, both within observational uncertainties. Crucially, unlike MOND—which postulates a fundamental acceleration scale—MIND predicts both the shape of the RAR and the physical location of the rotation-curve transition radius by solving π(r) = π₀. This prediction is confirmed across the full SPARC sample, with a Pearson correlation r = 0.964 (p < 10⁻²⁰) between predicted and observed transition radii and no residual trends with galaxy mass, scale length, or surface brightness. These results establish momentum coherence as a predictive, falsifiable physical mechanism underlying galaxy rotation curves, eliminating the need for dark matter halos or ad hoc acceleration scales at galactic scales.