How curved spacetime quietly destroys quantum superpositions

Starting from a particle with both internal and external (center-of-mass) quantum degrees of freedom coupled to a scalar field, a master equation is derived that governs how spatial superpositions decay along non-inertial but stationary worldlines. Two mechanisms contribute: the particle samples a modified field spectrum (analogous to the Unruh effect), and different branches of its wavefunction experience slightly different rates of time dilation. For hyperbolic and circular motion, both effects independently produce decoherence that looks thermal, giving a concrete, trajectory-dependent rate connecting quantum foundations to relativistic kinematics.