# Closed universe The Hilbert space of quantum gravity in a closed universe is one-dimensional. Once observers are introduced, however, the effective size can be much larger. ## Refs - non-perturbative path integral and observer Hilbert space - [[2025#Abdalla, Antonini, Iliesiu, Levine]] - [[2025#Harlow, Usatyuk, Zhao]] - [[2025#Akers, Bueller, DeWolfe, Higginbotham, Reinking, Rodriguez]] - [[2025#Chen]] - [[2025#Nomura, Ugajin]] - no-boundary proposal and observers - [[2025#Blommaert, Kudler-Flam, Urbach]]