How Gaussian can our Universe be?

Gravity is a non-linear theory, and hence, barring cancellations, the initial superhorizon perturbations produced by in ation must contain some minimum amount of mode coupling, or primordial non-Gaussianity. In single-eld slow-roll models, where this lower bound is saturated, non-Gaussianity is controlled by two observables: the tensor-to-scalar ratio, which is uncertain by more than fty orders of magnitude; and the scalar spectral index, or tilt, which is relatively well measured. It is well known that to leading and nextto- leading order in derivatives, the contributions proportional to the tilt disappear from any local observable, and suspicion has been raised that this might happen to all orders, allowing for an arbitrarily low amount of primordial non-Gaussianity. Employing Conformal Fermi Coordinates, we show explicitly that this is not the case. Instead, a contribution of order the tilt appears in local observables. In summary, the oor of physical primordial non-Gaussianity in our Universe has a squeezed-limit scaling of k2 ` =k2 s , similar to equilateral and orthogonal shapes, and a dimensionless amplitude of order 0:1 (ns 1).