# Black hole complementarity ## Refs - original - [[1993#Susskind, Thorlacius, Uglum]] - dynamical BH - [[2024#Concepcion, Nomura, Ritchie, Weiss]] - non-perturbative - [[2025#Engelhardt, Gesteau, Harlow]] ## A problem - Alice falls in but still has not reached the singularity, but Bob has already received the information Alice carries due to [[0217 Hayden-Preskill decoding criterion|Hayden-Preskill]] - then there is a Cauchy surface where there are two copies of a quantum diary; this violates the no-cloning theorem ## BH complementarity as a resolution - cannot find any way of collecting two copies at the same spacetime point - can check that it would take Planck energy to send such a message - i.e. no single observer can have two copies at the same ## Does this resolve everything? No. There is still a problem even for a single observer: see [[0195 Firewall|firewall]].