Observed universe mass-energy density is the density (critical density) that makes space curvature zero. If early-universe mass-energy density was 10^-14 more than early-universe critical density, later-universe density becomes much higher than later-universe critical density, and space becomes more curved and more closed. If early-universe mass-energy density was 10^-14 less than early-universe critical density, later-universe density becomes much lower than later-universe critical density, as space becomes less curved and more open. Therefore, because universe space curvature is zero now, early-universe space had zero curvature, an unlikely situation {flatness problem}. Perhaps, though early universe did not have critical density, early-universe cosmic inflation reduces space curvature.
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Date Modified: 2022.0224