For reasons to become apparent, let me interrupt here to say that many people ask how the Hubble expansion can fail to have a "central point" from which the expansion occurs.

Even in Newtonian dynamics, one can use transparencies to show that a dilation of form z -> exp(t) z is translation invariant (all points are equivalent).

But there's still a problem: as Olber noticed, if you use Newtonian theory to compute the intensity of starlight, assuming a homogeneous universe, the entire night sky should be as bright as the surface of the Sun. Obviously, it isn't. In Olber's time this was a profound mystery. With the advent of the Hot Big Bang theory, formulated gtr, it became apparent that repeating Olber's computation using a cosmological model such as an FRW dust solution of the EFE (the field equation of gtr), the expansion of the universe explains why the intensity of the night sky is much smaller than expected.

You are going to the opposite extreme and asking, I think, why the intensity is not below the threshold of measurement. One answer would be to say that when you crunch the numbers, it turns out not to be (in agreement with nightime experience for rural citizens). Another would be to say that in cosmological models featuring a sufficiently rapidly expanding universe, the intensity does indeed vanish in the limit as t -> infty.

Suggested reading:

• Olber's Paradox from Scott Chase, part of the UsetNet Physics FAQ, from John Baez (Mathematics, U.C. Riverside) and many others,
• Olber's Paradox, part of the Hyperphysics, website from Dept. of Physics & Astronomy, Georgia State University,
• Cosmology Tutorial from Ned Wright (Astronomy, UCLA),
• Cosmology FAQ from Ned Wright,
• 1995 Briefing from the National Academy of Science (not entirely out of date)
• Steven Weinberg, The First Three Minutes (same comment).

__________________
Chris Hillman

Read these PF posts. Avoid Wikipedia--- except for these versions. Read this and this suggested sticky. When asked for advice, I always say: never take advice!