Beyond linearized cosmology

We comment on the necessity of a unified approximative scheme within relativistic cosmology which would allow us to classify different cosmological models in a systematic way. We also report on recent progresses in formulating a cosmological post-Newtonian approximation and the problems related to such a scheme.Comment: 4 pages, 2 figures, to appear in the proceedings of the PASCOS 2005 symposium, Gyeongju, Korea, May 30 - June 4, 200