Smooth Causal Patches for AdS Black Holes

TL;DR

This paper resolves a paradox about low-energy excitations near AdS black holes by analyzing boundary operators and causal patches, showing that the paradox is avoided due to the position dependence of correlators and causal patch limitations.

Contribution

It demonstrates that the apparent paradox of creating large excitations with low energy near AdS black holes is resolved by causal patch considerations and correlator properties, providing a new perspective on AdS/CFT.

Findings

The paradox is resolved by the position dependence of boundary operators and bulk observables.

No observer can both create the excitation and observe its effect within a single causal patch.

The analysis applies to states with spontaneous excitations outside the infalling observer's causal patch.

Abstract

We review the paradox of low energy excitations about an AdS black hole. An appropriately chosen unitary operator in the boundary theory can create a locally strong excitation near the black hole horizon, whose global energy is small as a result of the gravitational redshift. The paradox is that this seems to violate a general rule of statistical mechanics, which states that an operator with energy parametrically smaller than $k T$ cannot create a significant excitation in a thermal system. When we carefully examine the position dependence of the boundary unitary operator that produces the excitation and the bulk observable necessary to detect the anomalously large effect, we find that they do not both fit in a single causal patch. This follows from a remarkable property of position space AdS correlators that we establish explicitly, and resolves the paradox in a generic state of the system, since no combination of observers can both create the excitation and observe its effect. As a special case of our analysis, we show how this resolves the "Born rule" paradox of arXiv:1506.01337 and we verify our solution using an independent calculation. We then consider boundary states that are finely tuned to display a spontaneous excitation outside the causal patch of the infalling observer, and we propose a version of causal patch complementarity in AdS/CFT that resolves the paradox for such states as well.