Geometric Decoherence: A Candidate Geometric Route to the Quantum-to-Classical Transition within the Zhang Effective Metric

We propose a geometric decoherence mechanism within the rotational-order unification framework built upon the Zhang Effective Metric. Stochastic zero-point fluctuations of the internal S³ orientation field generate fluctuations of the effective spacetime metric, imprinting random relative phases on quantum superpositions. The derived decoherence rate scales as M² at leading order, naturally suppressing macroscopic superpositions while preserving coherence for microscopic particles. This mechanism is qualitatively distinct from Diósi–Penrose / Károlyházy gravitational decoherence: the metric fluctuations originate from the internal fibre geometry rather than the mass distribution of the quantum system itself. The fluctuations couple only to massive matter-wave phases at leading order and do not produce photon dispersion. This work predicts a universal, shielding-insensitive noise floor for macroscopic quantum experiments.