This paper examines whether a globally defined quantum state can exist in cosmological spacetimes. The work explores how cosmological boundaries and horizon structures can prevent the construction of globally defined Hilbert space descriptions, suggesting that quantum descriptions of the universe may be fundamentally local rather than globally defined. The analysis investigates the implications of cosmological horizons, causal structure, and boundary constraints for the definition of global quantum information measures and quantum state evolution in cosmological systems.
Joquin Leyn Pillay (Mon,) studied this question.