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arXiv · 2008.05274

Entanglement between two disjoint universes

Vijay Balasubramanian·Arjun Kar·Tomonori Ugajin
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Abstract

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.

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Vijay Balasubramanian, Arjun Kar, Tomonori Ugajin. 2020-08-12. Entanglement between two disjoint universes. https://doi.org/10.1007/jhep02(2021)136

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