Friedmann–Lemaître universes and their metamorphoses

We analyze the dynamics of the Friedmann–Lemaître universes taking into account the different roles played by the fluid parameter and the cosmological constant, as well as the degenerate character of the equations. We find that the Friedmann–Lemaître system reduces to four qualitatively inequivalent normal forms and write down the sets of all stable perturbations that may result (the ‘versal unfoldings’). These sets are of small codimension up to three. We then describe all possible parameter-dependent solutions and their transfigurations to other forms during evolution through the bifurcation sets, these are also fully described. This analysis leads to a picture of cosmological evolution determined by new parameters related to codimension which are zero in standard cosmology. The emerging versal solutions are all free of singularities, while other properties of them are also discussed. © 2025 Elsevier B.V., All rights reserved.