The Friedmann equations only allow a constant a in the case where Λ is perfectly tuned relative to the other parameters, and even this artificially fine-tuned equilibrium turns out to be unstable. Th...The Friedmann equations only allow a constant a in the case where Λ is perfectly tuned relative to the other parameters, and even this artificially fine-tuned equilibrium turns out to be unstable. These considerations make a static cosmology implausible on theoretical grounds, and they are also consistent with the observed Hubble expansion.
