[Alamo-Girl]

Indeed, we cannot "see" the entire universe and can only measure to about 300,000 years after the Big Bang, when "the universe had cooled enough so that photons could "decouple" from electrons, protons, and neutrons; then atoms formed and light went on its way." (Harmonics in the Early Universe)

Concerning light, dimensions and time - we should spend more time discussing null paths.

By all indications though, the calculation of the age of the universe is accurate.

[RightWhale]

we cannot "see" the entire universe

Ignoring dark matter and all that, we not only can't see the entire universe, we can see so little that it could be rounded off to zero. We can see essentially none of the universe.

On that basis we assume the laws of physics are uniformly the same everywhere!