Black hole information and the Page curve

4 problems

• How does a single unitary theory avoid wormhole-induced ensemble averaging?

  Partially resolved

  The wormhole geometries used to get the Page curve also connect separate copies of a system, which normally happens only when one averages over many random theories. A single definite theory should not behave like an average, so something must cancel these wormhole effects.

• Do entanglement islands exist for evaporating black holes in ordinary 4D gravity?

  Contested

  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.

• Microscopic mechanism that makes Hawking radiation carry information out

  Partially resolved

  Calculations since 2019 show that the entropy of the radiation first rises and then falls back to zero (the Page curve), as quantum mechanics requires. Still missing is the physical account of how the information gets into the outgoing radiation, quantum by quantum.

• Can soft gravitational charges carry the information of an evaporating black hole?

  Partially resolved

  A black hole can carry tiny extra charges tied to zero-energy gravitons and photons, called soft hair. The question is whether this hair can store enough information to make evaporation information-preserving.