A consistent history is a POVM set of observables corresponding to a time-ordered product of projection operators. For gauge theories, not any old operator will do, only gauge-invariant observables. In quantum gravity, there are no localized observables, meaning observables have to be defined with respect to the conformal boundary. Inside a black hole, this is none other than the black hole singularity, which is often spacelike. Spacelike singularities are enigmatic in string theory. This raises the very interesting question; can we have consistent histories inside black holes?
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