Aspects of the Papadodimas-Raju Proposal for the Black Hole Interior

TL;DR

This paper critically examines the Papadodimas-Raju proposal for describing the black hole interior within AdS/CFT, highlighting its strengths, limitations, and conceptual challenges related to state interpretation and measurement.

Contribution

It clarifies the treatment of 1/N corrections, discusses the proposal's issues with state interpretation, and contrasts its state-dependence with standard quantum mechanics.

Findings

The proposal avoids some pitfalls of previous models.

States in the CFT do not have definite physical interpretations.

Measurement processes cannot be fully described by unitary evolution.

Abstract

In this note I elaborate on some features of a recent proposal of Papadodimas and Raju for a CFT description of the interior of a one-sided AdS black hole in a pure state. I clarify the treatment of 1/N corrections, and explain how the proposal is able to avoid some of the pitfalls that have disrupted other recent ideas. I argue however that the proposal has the uncomfortable property that states in the CFT Hilbert space do not have definite physical interpretations, unlike in ordinary quantum mechanics. I also contrast the "state-dependence" of the proposal with more familiar phenomena, arguing that, unlike in quantum mechanics, the measurement process (including the apparatus) in something like the PR proposal or its earlier manifestations cannot be described by unitary evolution. These issues render the proposal somewhat ambiguous, and it seems new ideas would be needed to make some version of it work. I close with some brief speculation on to what extent quantum mechanics should hold for the experience of an infalling observer.