QLunch: Niels Obers

The quest for a consistent theory of quantum gravity is one of the most important challenges in theoretical physics. In the landscape of physical theories, quantum gravity resides at the corner where all fundamental constants, Newton's constant, the speed of light, and Planck's constant are finite. Recently, it has become clear that there is rich physics at the edges of relativity, considering respectively the large (non-relativistic) and small (ultra-local or Carrollian) limits of the speed of light. These limits naturally lead to non-Lorentzian geometries, known as Newton-Cartan and Carrollian geometry, revealing a much richer structure of gravity than previously appreciated. I will introduce the physics and geometric formulation of these limits in the context of gravity, establishing their foundation.  At the end, I will briefly comment on their role in string theory and holography, highlighting recent advances.