I will explain how convex projective geometry over non-Archimedean ordered fields may be used to study large scale properties of individual real Hilbert geometries and degenerations of convex projective actions, using a projective geometry version of ultralimits. Non-Archimedean convex subsets have a naturally associated quotient Hilbert metric space. In the case of ultralimits, we show that it is the ultralimit of the real Hilbert metric spaces under a natural non-degeneracy condition. I will present some examples and give a full description of the Hilbert metric space for non-Archimedean polytopes defined over R, which correspond to the asymptotic cones of a fixed real polytope. This is joint work with Xenia Flamm.
Fanny Kassel