 Though of course the claim that the world forms a single entangled system will be controversial (as will any claim that involves an interpretation of quantum mechanics), in at least two respects. First, certain kinds of anti-realist and relationalist interpretations of quantum mechanics (e.g., Rovelli 1996) posit an irreducible relation between the quantum system and an external observer, which preclude assigning a quantum state to the whole world (for lack of an observer external to it). Secondly, some interpretations (e.g., Ghirardi-Rimini-Weber) posit a separate dynamics of wave-function collapse that breaks entanglements. But virtually any realist interpretation of quantum mechanics that also posits an initial singularity (the Big Bang) and unitary Schrödinger evolution will posit an entangled universe, since an initial singularity generates entanglement and Schrödinger evolution preserves it.