Islands in Closed and Open Universes

Understand

We show that spatial curvature has a significant effect on the existence of entanglement islands in cosmology.

• We consider a homogeneous, isotropic universe with thermal radiation purified by a reference spacetime.
• Arbitrarily small positive curvature guarantees that the entire universe is an island.
• Proper subsets of the time-symmetric slice of a closed or open universe can be islands, but only if the cosmological constant is negative and sufficiently large in magnitude.