Spacetime Geometry as a Modulator of Quantum Coherence: A Critical Velocity Perspective.

We propose that quantum coherence is fundamentally constrained by spacetime geometry. The coherence length L is determined by the smaller of two scales: a system’s physical size L_system or a curvature-dependent length L_curv, derived from the Ricci scalar R (matter-rich regions) or Kretschmann scalar K (vacuum). A critical velocity v_c = h/(mL) marks the threshold between quantum and classical regimes. Case studies in neutron stars, Bose-Einstein condensates (BECs), and strained graphene validate the model, demonstrating how curvature modulates coherence.