# Bulk point singularity The bulk point singularity happens in boundary 4-point or higher point functions when there exists a bulk point $p$ that is connected to the boundary points via null geodesics, even when the boundary points themselves are not null related with respect to the boundary metric. This is useful in holography because the singularity behaviour of the boundary correlators can tell us about the bulk geometry, known as [[0027 Bulk reconstruction using lightcone cuts|bulk reconstruction using lightcone cuts]]. Bulk point singularities (assuming their existence) can be used to extract flat space scattering amplitudes. ## Comments - c.f. [[0163 Bulk cone singularity|bulk cone singularities]] which happen for two-point functions; in that case this is no bulk *point* that leads to the singular behaviour ## Refs - original - [[2009#Gary, Giddings, Penedones]] - [[2009#Heemskerk, Penedones, Polchinski, Sully]] - beyond semi-classical geometry - [[2015#Maldacena, Simmons-Duffin, Zhiboedov]]: argues that non-perturbative theory had no bulk point singularity - limits and extensions - [[2019#Cardona]] eikonal limit, flat space amplitude - [[2025#Harvey, Jensen, Uzu]]: BCFT