# Cosmology parameters

Is the dark energy density calculated as follows: 1 – Matter Density Parameter?

• 1) On the SE, contrary to most forums and mailing lists, it is not a problem if you ask multiple questions, but they should be in different questions. So, feel free to ask 3 questions at once. 2) Here comes the second problem: SE won't be a wiki copy-paste site, thus some preliminary search is expected. Google for that, give more details what you searched, what you found, etc. – peterh Sep 3 '16 at 12:49

## 1 Answer

Is the dark energy density calculated as follows: 1 – Matter Density Parameter?

In good approximation, since the radiation and neutrino densities are small. The full form is

$$\Omega_{\Lambda}=\Omega_{\text{T}}-\Omega_{\text{M}}-\Omega_{\text{N}}-\Omega_{\text{R}}-\Omega_{\text{K}}$$

with $\Omega_{\Lambda}$ for the dark energy density, $\Omega_{\text{T}}$ the total density, $\Omega_{\text{M}}$ the nonrelativistic matter density, $\Omega_{\text{N}}$ the neutrino density, $\Omega_{\text{R}}$ the radiation density and $\Omega_{\text{K}}$ for the curvature.

Since $$\Omega_{\text{K}}=0 \to \Omega_{\text{T}}=1$$

so it simplifies to

$$\Omega_{\Lambda}=1-\Omega_{\text{M}}-\Omega_{\text{N}}-\Omega_{\text{R}}$$

• And how do they figure the curvature is 0? There is more to the story. – Bob Bee Sep 3 '16 at 20:49
• @Bob Bee: The curvature is determined by measuring the clump size in the CMB. For the actual results and error estimates see arxiv.org/abs/1502.01589 section 6.2.4 – Gendergaga Sep 3 '16 at 20:55
• Thanks. That's what I meant that it is a longer story. Besides the temperature spectrum a lot of modeling and fitting went into it. That arxiv article is a gem that everyone who has questions on how measured should be referenced to, imo. – Bob Bee Sep 3 '16 at 21:58