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I understand that dark matter only has a gravitational property. It does not interact directly with regular matter or EM radiation. The evidence for dark matter comes from observations that contradict known gravitational law. (Rotational velocity of galaxies that are far away is constant regardless of distance from galactic center). This and other data has indicated that dark matter only interacts through gravity.

Since gravitational lensing of light near black holes has been demonstrated, it is expected that large gravitational distortions from dark matter can also distort light. Has this been seen?

Can the increasing redshift of light with distance be explained by the cumulative of effect dark matter exerting a gravitational force that is directed away from us?

Another way to think about this is to consider that our observable universe has a fixed dimension. There has not been enough time for light to reach us from stars beyond that dimension. However, if the actual universe were much larger than the observable universe, and it was all filled with dark matter, would we not see its gravitational effect on light that was emitted from the boundary that we can see? (as long as the dark matter was not homogeneous) This following explanation suggests that dark matter homogeneously distributed in the cosmos can not have gravitational effects. http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshell2.html

Basically, the force from any spherically symmetric mass distribution on a mass inside its radius is zero.

So that means that dark matter is not homogeneous in the universe. The density of dark matter has been calculated as well.

http://scitechdaily.com/astronomers-measure-the-density-of-dark-matter-in-galaxy-clusters/

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How much dark matter is needed to gravitationally distort light?

The same amount like normal matter. If you had a bunch of dark matter with a mass equal to our sun's, a light ray passing this mass in a distance of one solar radius would get deflected by the same 1.75" light gets deflected when it edges our normal mattered sun (assuming that the radius of the dark mass is equal to or less than our sun's). (1)

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    $\begingroup$ The distortion of distant galaxies due to dark matter has been measured, and has been used to create maps of dark matter around particular nearby galaxies. $\endgroup$
    – rob ♦
    Feb 15, 2015 at 4:47
  • $\begingroup$ thank you rob for that citation. In light (no pun intended) of that article, the specific question I wanted to ask is this: is the light coming THROUGH the dark matter red shifted compared to light from an adjacent sources passing just near the dark matter? $\endgroup$
    – aquagremlin
    Feb 15, 2015 at 21:00
  • $\begingroup$ My understanding may be flawed, but my question assumes that dark matter does not interact with regular matter or EM radiation except through gravity. (so dark matter is truly transparent.) $\endgroup$
    – aquagremlin
    Feb 15, 2015 at 21:11
  • $\begingroup$ And since dark matter does not interact with regular matter, can it be said to have mass? I thought dark matter was something different than heavy space dust. And we are calculating its 'mass' based on optical distortion, rather than other more direct means. I thought dark matter produces gravity without having mass or optical properties. $\endgroup$
    – aquagremlin
    Feb 15, 2015 at 21:18
  • $\begingroup$ Dark matter does not interact via electromagnetic forces. It can interact via gravity and maybe also the weak force (therefore they call one candidate wimp, which means weakly interacting particle). $\endgroup$
    – Yukterez
    Feb 16, 2015 at 14:26
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There is not dark matter. There is matter with (non/ negative) divergence. Dark matter (neutron Cooper pairs) is isolated system (There are not fluctuation in dark matter area) and impact neutrino are aprox. 2-3 kelvin degree. There is a scalar field because "dark matter" particle attenuated neutrinino flux.

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    $\begingroup$ This is nonsense. $\endgroup$
    – ACuriousMind ♦
    Feb 15, 2015 at 18:09
  • $\begingroup$ ACuriousMindIn actual paradigm,YES. but $\endgroup$
    – crivoi D
    Feb 15, 2015 at 19:27
  • $\begingroup$ That comment (by crivoi D) is probably written by a flawed copy of Weizenbaum's Eliza. It does not have the syntax or grammar that a human would use. Or perhaps one of those prose writing programs that produce gibberish? $\endgroup$
    – aquagremlin
    Feb 15, 2015 at 21:13
  • $\begingroup$ "The density of dark matter depends on the properties of the individual dark matter particles, just like the density of everyday materials depends on what they are made of. CDM – the most successful dark matter theory to date – predicts that dark matter particles only interact with each other and with other matter via the force of gravity, they don’t emit or absorb light." IN ACCORD WITH MODERN PARADIGM- "The electroconvergence o natural bodies" $\endgroup$
    – crivoi D
    Feb 16, 2015 at 11:40

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