New York University, October 6, 1:00 pm
The formulation of a complete theory of quantum gravity remains a fundamental open problem in modern physics. Meaningful progress has arisen from concrete realizations of the holographic principle, which is a conjectured equivalence between systems of quantum gravity and ordinary non-gravitational systems in fewer dimensions. At present, this principle is best understood in the context of negatively-curved spacetimes. Celestial holography – the subject of this lecture – is a novel extension of the holographic approach to the asymptotically flat context. More specifically, it is a proposed equivalence between gravitational scattering in asymptotically flat spacetimes and a conformal field theory living on the celestial sphere. Remarkably, the process of so-reformulating the physics has unearthed new structure that underlies the gravitational scattering problem. Notably, gravitational scattering admits an infinite-dimensional symmetry, which has been now identified as the w(1+infinity) symmetry that has previously appeared in other two-dimensional physical systems. These symmetries imply an infinite number of constraints on scattering amplitudes, which physically enforce universal behavior in the infrared.