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by uts 3977 days ago
The paradox says that an universe infinite in space and time would have to be bright in all directions. By infinite in time, I mean that the universe has been around infinitely long, i.e. it has no beginning. The finite speed of light wouldn't matter here since the light would have had an infinite amount of time to reach you.
1 comments

Huh? We definitely know that that doesn't describe the universe. If two points are so far apart that the expansion of space inflates the distance between them faster than light can cross it, then no light can ever reach from one to the other, even if it travels for an infinitely long time.
The Olbers' paradox is from the 1800s, before we knew about the expansion of space. It's arguing against a static, infinitely old universe. As you point out, we now know that this isn't the case.
> If two points are so far apart that the expansion of space inflates the distance between them faster than light can cross it, then no light can ever reach from one to the other, even if it travels for an infinitely long time

Actually, it can. The issue is quite subtle. What you are saying is true only if the Hubble parameter is constant, it is not. (Hubble constant is such a misnomer! It's only constant across space but not time).

You may want to re-read paragraph 3.3 of the Lineweaver paper (http://arxiv.org/pdf/astro-ph/0310808v2.pdf)

Quotes :

> Photons near the Hubble sphere that are receding slowly are overtaken by the more rapidly receding Hubble sphere.

> The most distant objects that we can see now were outside the Hubble sphere when their comoving coordinates intersected our past light cone. Thus, they were receding superluminally when they emitted the photons we see now.

We know, but Olbers didn't. He died in 1840.