$Ω$ is taken to have different components - ordinary matter, dark matter, dark energy. But because it is expressed in relation to the critical density for attractive gravity, it seems that omega is expressed as if all the gravity it contains is attractive.

As we observe an accelerating expansion, what is the estimated value for omega? It seems it must be some number just below 1.


1 Answer 1


$1-\Omega=0$ for a spatially flat Universe -- it has nothing to do with the presence or absence of dark energy. All observations to date are consistent with a spatially flat universe. The results quoted in the abstract of the 2018 Planck paper [1] say $1-\Omega = \Omega_k = 0.001 \pm 0.002$, where $\Omega_k$ is the fraction of the critical density in spatial curvature.

[1] https://arxiv.org/abs/1807.06209

  • $\begingroup$ Thank you. I'll look through these. Have a good evening. $\endgroup$
    – user141183
    Mar 23, 2022 at 1:40
  • 1
    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – rob
    Mar 23, 2022 at 16:04

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