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arXiv · 2103.14364

Islands and mixed states in closed universes

Seamus Fallows·Simon F. Ross
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Abstract

We investigate the appearance of islands when a closed universe with gravity is entangled with a non-gravitating quantum system. We use braneworlds in three-dimensional multiboundary wormhole geometries as a model to explore what happens when the non-gravitating system has several components. The braneworld can be either completely contained in the entanglement wedge of one of the non-gravitating systems or split between them. In the former case, entanglement with the other system leads to a mixed state in the closed universe, unlike in simpler setups with a single quantum system, where the closed universe was necessarily in a pure state. We show that the entropy of this mixed state is bounded by half of the coarse-grained entropy of the effective theory on the braneworld.

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Seamus Fallows, Simon F. Ross. 2021-03-26. Islands and mixed states in closed universes. https://doi.org/10.1007/jhep07(2021)022

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