# Gao-Wald theorem The Gao-Wald theorem states that [[0480 Null energy condition|NEC]] implies [[0091 Boundary causality|boundary causality in AdS]]. The fastest route between two points on the boundary of AdS stays on the boundary, i.e., there is not short cut through the bulk. ## Related - [[0091 Boundary causality]] ## Refs - OG: [[2000#Gao, Wald]] - generalisations - Galloway: see footnote 1 (from privative conversations with Galloway); allows generalisation to [[0006 Higher-derivative gravity]] - further variation - [[MoralesSantillan2021]][](https://arxiv.org/pdf/2004.12523.pdf)