# Is the whole universe a closed quantum system?

By the whole universe I mean everything besides $$|0\rangle$$, if not what is the environment then? How do they interact?

If the whole universe is a closed system, can we assign a single Hamiltonian to it?

• I'm not sure anybody knows the answers. Here are a couple of papers that corroborate this, both by well-respected physicists. Regarding the "environment" question, see Bousso and Susskind, "The Multiverse Interpretation of Quantum Mechanics", arxiv.org/abs/1105.3796. Regarding the "single Hamiltonian" question, see Banks, "TASI Lectures on Holographic Space-Time...", arxiv.org/abs/1007.4001. Both papers are speculative, and that's the point: I'm not sure anybody knows the answers. – Chiral Anomaly Nov 21 '18 at 16:02