Entropy bound and the non-universality of entanglement islands

TL;DR

This paper investigates the possibility of a universal entanglement island supporting all AMPS-relevant radiation regions, concluding that such universality is obstructed by entropy bounds, thus requiring region-dependent interior reconstructions.

Contribution

It demonstrates that a universal compact entanglement island cannot exist without violating entropy bounds, highlighting the region-dependent nature of interior reconstruction in the island framework.

Findings

Universal islands accumulate entropy exceeding Bekenstein-Hawking bounds.

A semiclassical island can exist for at least one radiation region.

Interior reconstruction must be region-dependent, not universal.

Abstract

Entanglement islands resolve the AMPS firewall paradox in a region-dependent manner by modifying the entanglement wedge of Hawking radiation. We investigate whether this resolution can be made universal, in the sense that a single compact island serves as a common interior support for all AMPS-relevant radiation regions. We show that such a construction is obstructed under reasonable assumptions. Universality forces an accumulation of interior partner entropy within a fixed compact region, which at late times exceeds the Bekenstein--Hawking bound set by its boundary area. However, a bona fide semiclassical island realization for at least one radiation region is expected to be compatible with semiclassical entropy bounds. This leads to a contradiction, yielding a conditional no-go result for universal compact islands. Our result implies that interior reconstruction in the island framework must remain intrinsically region-dependent.