Entanglement between two disjoint universes

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