Do entanglement islands exist for evaporating black holes in ordinary 4D gravity?
In plain words
The island calculation assigns a region inside the black hole to the distant radiation. It is unclear whether this works when gravity acts everywhere with a massless graviton, as in our universe, instead of in model setups where the radiation escapes into a region without gravity.
Precise statement
Consider a 4D asymptotically flat Schwarzschild black hole evaporating to null infinity, with dynamical massless gravity everywhere and no non-gravitating bath. Does the prescription S(R) = min ext_I [A(boundary of I) c^3/(4 G hbar) + S_bulk(R u I)] with a nontrivial island I give a well-defined, gauge-invariant entropy for a radiation region R that follows the Page curve? Answer yes with a construction of R and I compatible with the gravitational Gauss law, or no with a proof that islands require a massive graviton or a non-gravitating region.
What would settle it
A gauge-invariant definition of the radiation algebra at null infinity together with a computation of its entropy, or a no-go theorem from the gravitational constraints.
Status in the literature
Unverified note
Arguments that islands require massive gravity (Geng and Karch 2020, extended 2025) and defenses of islands in massless gravity (2025) both stand as of 2026.