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Re: Old Stars/Olber's Paradox




Jim G. wrote:
...
So somebody please tell me why the sky is dark -- in view of this discussion
about "Old Stars, quasars, and Q's flashlight.

There are 4 possible suggested mechanisms (that I can think of) as to why the
sky would be dark in most directions.
1) The universe is finite in spatial extent giving only a finite number of
point light sources.
2) The universe is finite in time. Since it has only been around for a finite
amount of time there is a light-travel-time-since-the-beginning horizon beyond
which no light can be seen.
3) The universe is expanding--causing the light from the most distant sources
to be red-shifted away to ever lower (& dimmer) photon energies.
4) The luminous matter of the universe is hierarchically arranged in a fractal
arrangement whose Hausdorff dimension is less than 3 so that the sources of
light are a set of measure zero in space (yielding an average density of zero)
allowing there to be not enough light sources to light up the sky in most
directions.

There was a debate a while ago in cosmological circles as to
which of these two mechanisms, 2) or 3), is dominant in making the sky dark.
A few years ago a consensus developed as to which one was more important, but
I can't remember which way it came out. (Maybe a legitimate list-resident
general relativist can help us out here.)

Mechanism 2.


Paul J. Camp "The Beauty of the Universe
Assistant Professor of Physics consists not only of unity
Coastal Carolina University in variety but also of
Conway, SC 29526 variety in unity.
pjcamp@csd1.coastal.edu --Umberto Eco
pjcamp@worldnet.att.org The Name of the Rose
(803)349-2227
fax: (803)349-2926