On the Breakdown of Unitary Evolution Across Cosmological Boundaries

This paper investigates the breakdown of globally unitary quantum evolution in cosmological spacetimes containing horizons and causal boundaries. In such settings, quantum states defined within one causal region may not evolve unitarily when considered across the full cosmological manifold. The analysis explores how cosmological horizons and boundary constraints restrict the ability to construct globally consistent unitary evolution operators. The results suggest that quantum evolution in cosmological systems may need to be described through locally defined dynamical frameworks rather than globally unitary evolution across the entire spacetime.