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So, this bit of information confused me lately. Before, I figured galaxies were no longer visible by us because their luminosity decreased in an inverse square manner. However, while watching a movie I stumbled upon the concept of how galaxies disappeared from our sight because the space which both galaxies occupy is moving away from each other faster than the speed of light.

I understand nothing can move faster than the speed of light, but the argument here, I guess, is that space itself can move, as a consequence of the Big Bang, faster than the speed of light. Is this correct? If not, how do galaxies disappear?

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    $\begingroup$ What is the question here? You haven't asked anything in the paragraph you wrote, and you answered the title question yourself: spatial expansion carries distant galaxies away faster than light, which doesn't run afoul of relativity since nothing is moving through space FTL. $\endgroup$
    – user27578
    Commented Feb 26, 2014 at 3:28
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    $\begingroup$ Sorry about that! My question is, which of this is correct (which you mentioned was spatial expanssion) and hoe can we proove that. $\endgroup$
    – Demian Licht
    Commented Feb 26, 2014 at 11:25
  • $\begingroup$ Well, it isn't either/or. Stellar magnitude (luminosity is a fixed quantity and doesn't change with distance) also restricts what's visible to any particular light-collecting device, like eyes or telescopes. As for the evidence in favour of cosmological expansion (we don't prove things in science), that is much, much too broad for physics.SE. $\endgroup$
    – user27578
    Commented Feb 26, 2014 at 17:09

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It would be more correct to say that distant galaxies appear than to say they disappear. Based upon the accepted big bang theory, there are galaxies that formed early in the universe from which light has not yet reached us, but that will reach us in the future. On the other hand, accelerating expansion of the universe could cause light emitted after a certain time from a galaxy currently visible to never reach us; however, increasingly red-shifted, ever dimmer light from such a galaxy would continue to be observed.

References:

http://www.cfa.harvard.edu/seuforum/faq.htm

http://arxiv.org/pdf/astro-ph/0107568v2.pdf

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