We are interested in observing the average of various quantities, such as those corresponding to the cosmological parameters. However, all we can do is average our observations along several lines of sight. The relationship between these two things is in general complicated. Since the m-z relation for Type Ia supernovae indicates that the universe is close to being homogeneous, even on small scales, the question arises whether this is some sort of average over all the lines of sight involved or whether each line of sight is close to being a fair sample of the universe.
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