 Lack of knowledge of the full space of solutions to EFE makes it difficult to assess the fragility of various inferences cosmologists make based on perturbed FLRW models. A fragile inference depends on the properties of the model holding exactly, contrasted with robust inferences that hold even if the models are good approximations (up to some tolerable error) that will hold even if the model is perturbed. The singularity theorems (Hawking &amp; Ellis 1973), for example, establish that the existence of an initial singularity is robust: rather than being features specific to the FLRW models, or other highly symmetric models, singularities are generic in models satisfying physically plausible assumptions. The status of various other inferences cosmologists make is less clear. For example, how sensitively does the observational case in favor of dark energy, which contributes roughly 70% of the total energy density of the universe in the SM, depend upon treating the universe as having almost-FLRW spacetime geometry? As mentioned above, recent work has pursued the possibility of accounting for the same observations based upon large-scale inhomogeneities or local back-reaction, without recourse to dark  energy.[12]  Studies along these lines are needed to evaluate the possibility that subtle dynamical effects, absent in the FLRW models, provide alternative explanations of observed phenomena. The deduction also depends on the assumption that the EFE hold at cosmological scales - which may not be true: maybe for example some form of scalar-tensor theory should be used. More generally, an assessment of the reliability of a variety of cosmological inferences requires detailed study of a larger space of cosmological models.