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If general relativity accounts for a redshift, independent of inflation, how can we still know that inflation is viable? Moreover, how do we differentiate the the gravitational redshift and the cosmological redshift observationally?

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  • $\begingroup$ I once happened to ask this same question in APOD. The answers given by astronomers/physicists there may add something worthwhile to the discussion here. $\endgroup$ – Jyrki Lahtonen Oct 31 '14 at 14:14
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The cosmologial redshift only requires expansion, not inflation.

There is no way to distinguish just from observing the light of a single object how much of the shift is cosmological, gravitational or Doppler (peculiar motion).

However, given that in all directions the red shift is increasing rather uniformly with distance, expansion seems like the only explanation. To be all gravitational, the objects would need to be uniformly at lower gravitation potential as distance from Earth increases.

See this Stanford link for more infomation: http://einstein.stanford.edu/content/relativity/a11859.html

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