  We study two disjoint universes in an entangled pure state. When only one
universe contains gravity, the path integral for the $n^{\text{th}}$ R\'enyi
entropy includes a wormhole between the $n$ copies of the gravitating universe,
leading to a standard "island formula" for entanglement entropy consistent with
unitarity of quantum information. When both universes contain gravity,
gravitational corrections to this configuration lead to a violation of
unitarity. However, the path integral is now dominated by a novel wormhole with
$2n$ boundaries connecting replica copies of both universes. The analytic
continuation of this contribution involves a quotient by $\mathbb{Z}_n$ replica
symmetry, giving a cylinder connecting the two universes. When entanglement is
large, this configuration has an effective description as a "swap wormhole", a
geometry in which the boundaries of the two universes are glued together by a
"swaperator". This description allows precise computation of a generalized
entropy-like formula for entanglement entropy. The quantum extremal surface
computing the entropy lives on the Lorentzian continuation of the cylinder/swap
wormhole, which has a connected Cauchy slice stretching between the universes
-- a realization of the ER=EPR idea. The new wormhole restores unitarity of
quantum information.
