The Multiverse in an Inverted Island

Understand

We study the redundancies in the global spacetime description of the eternally inflating multiverse using the quantum extremal surface prescription.

• We argue that a sufficiently large spatial region in a bubble universe has an entanglement island surrounding it.
• Consequently, the semiclassical physics of the multiverse, which is all we need to make cosmological predictions, can be fully described by the fundamental degrees of freedom associated with certain finite spatial regions.
• The island arises due to mandatory collisions with collapsing bubbles, whose big crunch singularities indicate redundancies of the global spacetime description.