 It is mathematically equivalent to a special case of the FLRW model in the limit of zero energy density (in other words, an empty universe) and it obeys the cosmological principle.The Milne model is also similar to Rindler space, a simple re-parameterization of flat Minkowski space.Since it features both zero energy density and maximally negative spatial curvature, the Milne model is inconsistent with cosmological observations.