Celestial Holography

In modern physics, formulating a complete theory of quantum gravity remains one of the biggest challenges. As a new approach to probe quantum gravity, the quest for flat space holography has recently received a boost. The primary goal of Celestial Holography is to extend the holographic principle to asymptotically flat spacetimes like the one we inhabit. 

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Recent discoveries unveiled and extended the equivalence between the Ward Identity of asymptotic symmetries identified by BMS, soft graviton theorem by Weinberg, and gravitational memory by Polnarev and Zeldovich. The extended synthesis implies that the 4D asymptotically flat quantum theory of gravity is governed by an infinite tower of symmetries, where BMS supertranslation and the local conformal group on the celestial sphere at null infinity (also called superrotation) fills the first two entries in the tower. The second entry motivates Celestial Holography to aim for a duality between quantum gravity in asymptotically flat spacetime and a codimension-two celestial conformal field theory (CCFT), which naturally touches on a number of disparate fields and has been developed in a wide variety of directions.