Expanding Singularities and C^0-(in)extendibiltiy

We introduce the concept of an "expanding singularity" in a globally hyperbolic spacetime, characterised by asymptotic blowup of the (Riemannian) diameter of certain subsets of Cauchy hypersurfaces. Such singularities are present in Kasner and Gowdy spacetimes for example. We show that C^0 extensions across expanding singularities must have a boundary that is non-compact and null almost everywhere.