“FIREWALLS, like reversals of the second law, can occur in one of two ways; either by the action of an extremely complex operation needed to locally reverse the arrow of time, or by bottling up the system for a classical recurrence time. Temporary firewalls can also form if black holes are formed over long time periods.”
https://onlinelibrary.wiley.com/doi/full/10.1002/prop.201500092?casa_token=8OO3b1OY4e4AAAAA%3ARqriAgTwtxnvsxl09CqnNy79m7l4ye7ZrkZxcLtObB9kHsTwYgzBuIV2X-xXQ7ezoR6VQPfQLCS-vnI