Question

In the Big Bang model with an initial singularity, distant regions of the universe that we observe today with the cosmic microwave background radiation were never in communication with each other in the past. How is it that the temperature of the CMB is so uniform?

Answer 1

After sometime from big bang,

It is manifested that universe had gone through a phase of very rapid expansion in which our observable universe expanded 60 folds in a flash of time diluting certain observables of the present universe and making cosmic microwave background homogeneous such that it corresponds to roughly a same value of temperature along all directions such that before expansion they were in thernal contact.

This process of rapid expansion is known as inflation.

And this horizon problem of uniform temperature was successfully explained by inflation.