Black hole interiors and the firewall problem

5 problems

• Does interior volume growth equal computational complexity of the dual state?

  Contested

  The volume inside an eternal black hole keeps growing for an extremely long time, long after the outside has settled down. One proposal ties this growth to the growing complexity of the quantum state that describes the black hole.

• Is decoding interior partners from Hawking radiation exponentially hard?

  Partially resolved

  An observer who wants to test the firewall argument must first extract one particular quantum from the radiation, a very hard computation. If it takes longer than the black hole lives, the paradox can never be tested.

• Does an infalling observer see vacuum at an old black hole's horizon?

  Contested

  A 2012 argument showed that information preservation, normal physics outside the black hole, and a smooth horizon cannot all hold once a black hole has emitted half its entropy. Which assumption fails is still debated.

• Are typical black hole microstates horizonless geometries?

  Contested

  The fuzzball proposal says each microscopic state of a black hole is a horizonless tangle of strings and branes, so there is no interior at all. The known smooth examples account for far fewer states than the black hole entropy requires.

• Must the black hole interior be reconstructed by state-dependent operators?

  Contested

  To describe the inside of a black hole using only outside quantities, some proposals let the translation rules depend on which quantum state the black hole is in. Critics argue that this conflicts with the linearity of quantum mechanics.