Quote:
Originally Posted by Greeksquared
Isn't it possible that all the light that we observe has yet to reach us? and could this unobserved part of the universe be responsible for what we call dark matter?
No. Dark matter was first proposed (or at least was applied early on) to explain the rotational velocity of galaxies. Essentially, stars weren't going at the speed they 'should' if all the mass of a galaxy was visible matter.
Second, experiments on the CMB, using visible light (visible in the mechanical sense, not to the human eye) from just after the big bang shows evidence of dark matter. Though I'm not sure that's as convincing as the first.
Actually, this quote from Wiki pretty much summarizes things:
"Dark matter was postulated by Fritz Zwicky in 1934 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe; these observations include the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies."
All of these are indications of dark matter in the visible universe, and not something outside the visible universe.