# Bulk reconstruction **Bulk reconstruction** is the idea of obtaining bulk quantities (including the metric) using data on the boundary. The data could be e.g. entanglement entropy, $n$-point functions, and etc. ## Different approaches - [[0016 HKLL|HKLL]] - hard problem in practice and sometimes not well-defined - using entanglement - assume a semiclassical bulk - [[2019#Bao, Cao, Fischetti, Keeler]] - \[13-26\] of [[HashimotoWatanabe2021]] - using [[0027 Bulk reconstruction using lightcone cuts|lightcone cuts]] - can test whether the bulk is semiclassical given only knowledge in CFT - using [[0204 Quantum complexity|complexity]] - [[HashimotoWatanabe2021]]: can construct BH interior - inversion formula - [[2020#Hashimoto]] - discrete model - [[AaronsonPollack2022]][](https://arxiv.org/pdf/2210.15601.pdf) - generalised free fields - [[2023#Nebabu, Qi]] - explicit [[0421 Higher-spin gravity|higher spin gravity]] reconstruction from $O(N)$ model - [[2023#Koch]] ## Other things that can be reconstructed - constructing the bulk observer's experience - [[2020#Jafferis, Lamprou]] - something similar to AdS/CFT - [[GrimmMonneeVanDeHeisteeg2022]][](https://arxiv.org/pdf/2103.12746.pdf) - de Sitter - [[2024#Goldar, Kajuri]]: resolves issues for higher-spin fields