Horizon

Horizon Problem

The horizon problem arises because light moves with a finite speed. As a result, certain events which occur in the Universe are completely independent of each other,

The current Universe has a horizon distance of

A simple calculation indicates that at the time of recombination, material which was in causal contact (able to communicate) are currently separated by around 0.8 angular degrees on the sky. this means that the sky could only mix over separations of 0.8 degrees and so, there is no rational reason to believe that the sky should look the same everywhere! This is the Horizon Problem.

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