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#31




Dark matter is:
In article ,
jacobnavia writes: If the sea of galaxies extends to infinity (or to huge distances) the farther you look, the more galaxies you will observe for a given solid angle. At great distances you will see a wall of galaxies that fills completely the view. The (very redshifted) light from those galaxies is the CMB. As JT pointed out, this is closely related to Olbers' Paradox; the resolution of which is well known. The point is that the "light from these galaxies" cannot fit the spectral energy distribution (SED) of the CMB. If you don't know what an SED is, have a look at http://coolwiki.ipac.caltech.edu/index.php/SED_plots which defines it. (The article is oversimplified in places, and I don't agree with the "Units Matter" section, but the definition of SED and basic explanation of it are accurate.) "Sea of galaxies" was a possible model for the CMB until COBE flew, but that model is inconsistent with COBE and later data.  Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 6174957123 Cambridge, MA 02138 USA 
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#32




Dark matter is:
On Tuesday, 7 November 2017 00:19:18 UTC+1, Phillip Helbig wrote:
You don't need a simulation. There is acceleration if Omega/2  lambda 0. Which are the present values for Omega and Lambda? When you visit https://lambda.gsfc.nasa.gov/toolbox/tb_camb_form.cfm they use Omega(b), Omega(c), Omega(nu) and Omega(k) Lambda is not mentioned. This makes it tricky to decide if the above formule is a good yardstick. Nicolaas Vroom [[Mod. note  Ned Wright's cosmology tutorial is excellent: http://www.astro.ucla.edu/~wright/cosmolog.htm  jt]] 
#33




Dark matter is:
In article ,
Nicolaas Vroom writes: On Tuesday, 7 November 2017 00:19:18 UTC+1, Phillip Helbig wrote: You don't need a simulation. There is acceleration if Omega/2  lambda 0. Which are the present values for Omega and Lambda? Omega = 0.3, lambda = 0.7. When you visit https://lambda.gsfc.nasa.gov/toolbox/tb_camb_form.cfm they use Omega(b), Omega(c), Omega(nu) and Omega(k) Lambda is not mentioned. The dynamics of the universe depend on the total value of Omega, dark matter, baryons, etc. If you're interested in the contents, then it makes sense to have different symbols, otherwise you have to add them all up. In one notation (unfortunately, there are several) Omega_M + Omega_Lambda + Omega_K = 1 or Omega + lambda + Omega_L = 1 Hence Omega + lambda = 1 if the universe is flat. Yes, different notation schemes can be confusing, on the other hand understanding them can help one learn other things. 
#34




Dark matter is:
In article , "Phillip Helbig (undress to
reply)" writes: In one notation (unfortunately, there are several) Omega_M + Omega_Lambda + Omega_K = 1 or Omega + lambda + Omega_L = 1 Above line should be Omega + lambda + Omega_K = 1 Hence Omega + lambda = 1 if the universe is flat. Yes, different notation schemes can be confusing, on the other hand understanding them can help one learn other things. In the scheme above, Omega_K := 1  Omega  lambda or Omega_K := 1  Omega_M  Omega_lambda One can also find Omega_K := Omega_M + Omega_lambda  1 or Omega_K := Omega + lambda  1 i.e. the sign of Omega_K is opposite. I prefer the latter, since then Omega_K (or K, in some notation) has the same sign as k, the curvature constant in the Friedmann equation. 
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