Solving the smooth-photon problem means finding a way for those early photons (the ones coming from different ends of the universe) to have mixed so they could even out in temperature; this can happen only if—at some time in the distant past—those photons were much closer to one another than the current rate of expansion predicts. Inflation solves this problem by saying that the photons were indeed closer together at some point before the rapid expansion of space-time. Before inflation, the universe was small enough that there was time for all those photons to get to know each other and
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