A physical protocol for observers near the boundary to obtain bulk information in quantum gravity

We consider a set of observers who live near the boundary global AdS, and are allowed to act only with simple low-energy unitaries make measurements in small interval time. The not leave near-boundary region. describe physical protocol that nevertheless allows these obtain detailed information about bulk state. This utilizes leading gravitational back-reaction excitation on metric, also relies entanglement-structure vacuum. For states, we show how can use this completely identify explain why fails theories without gravity, including non-gravitational gauge theories. provides perturbative evidence for claim one signatures holography - fact is available already visible theory gravity.