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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 a

by uts 11y 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.

thaumasiotes 11y ago
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.
- Someone 11y ago
  We know, but Olbers didn't. He died in 1840.
- uts 11y ago
  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.
- jobigoud 11y ago
  > 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 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.

by uts 11y ago

thaumasiotes 11y ago

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.

Someone 11y ago
We know, but Olbers didn't. He died in 1840.
uts 11y ago
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.
jobigoud 11y ago
> 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 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.