This paper introduces a semi-classical gravitational framework in which spacetime curvature is sourced not only by realized mass-energy, but also by the probability amplitudes of uncollapsed quantum states. The theory predicts that the gravitational field responds not only to realized mass-energy, but also—transiently—to quantum probability amplitudes before collapse, with measurable effects in macroscopic systems that maintain partial coherence. This reinterpretation offers an alternative to particle-based dark matter by proposing that observed gravitational anomalies—such as flat galaxy rotation curves and mass distributions inferred from gravitational lensing—arise from decoherence-modulated probabilistic curvature. A central prediction is that high-entropy, quantum-informational systems should exert measurably more gravitational influence than inert systems of equal rest mass. The theory is formalized through a toy model extension of Einstein’s field equations, introducing a decay-weighted probabilistic stress-energy term ( T^{text{prob}}_{muu} ), derived from the amplitude structure of quantum states. A phenomenological decoherence function ( Gamma(E) ) is introduced and constrained using astrophysical data. Three falsifiable tests against SPARC rotation curve data are presented:begin{itemize} item A derived probability field density ( ho_0^Q ) shows consistent scaling with baryonic mass, item A modified acceleration law reproduces Milgrom-like behavior without invoking new particles, item The parameter-free fit across diverse galaxies yields low ( chi^2 ) residuals compared to $Lambda$CDM.end{itemize}The framework also addresses gravitational lensing in the Bullet Cluster and reframes the black hole information paradox by treating singularities as null probability domains. While speculative, the model introduces no new particles or ontologies and remains grounded in established physics. It is offered as a testable augmentation to general relativity—a bridge between quantum uncertainty and gravitational geometry that reframes what mass is, and when it matters.