Anisotropic universes with isotropic cosmic microwave background radiation

We show the existence of spatially homogeneous but anisotropic cosmological models whose cosmic microwave background temperature is exactly isotropic at one instant of time but whose rate of expansion is highly anisotropic. Although these models require fine-tuning, they nevertheless show that the observation of a highly isotropic cosmic microwave background temperature cannot alone be used to infer that the universe is close to a Friedmann–Lemaitre model since the time of last-scattering.