Entanglement between two disjoint universes

• Published in: The journal of high energy physics Vol. 2021; no. 2; pp. 1 - 27
• Main Authors: Balasubramanian, Vijay, Kar, Arjun, Ugajin, Tomonori
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2021; Springer Nature B.V; Springer Nature; SpringerOpen
• Subjects: 2D Gravity; AdS-CFT Correspondence; ASTRONOMY AND ASTROPHYSICS; Black Holes; Classical and Quantum Gravitation; Conformal Field Theory; Cosmological constant; Elementary Particles; Entanglement; Entropy; Geometry; Gravitation; Gravity; High energy physics; High temperature; Islands; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Radiation; Regular Article - Theoretical Physics; Relativity Theory; String Theory; Universe; Wormholes; AdS-CFT Correspondence; 2D Gravity; Black Holes; Conformal Field Theory
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP02(2021)136

A bstract We use the replica method to compute the entanglement entropy of a universe without gravity entangled in a thermofield-double-like state with a disjoint gravitating universe. Including wormholes between replicas of the latter gives an entropy functional which includes an “island” on the gravitating universe. We solve the back-reaction equations when the cosmological constant is negative to show that this island coincides with a causal shadow region that is created by the entanglement in the gravitating geometry. At high entanglement temperatures, the island contribution to the entropy functional leads to a bound on entanglement entropy, analogous to the Page behavior of evaporating black holes. We demonstrate that the entanglement wedge of the non-gravitating universe grows with the entanglement temperature until, eventually, the gravitating universe can be entirely reconstructed from the non-gravitating one.