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From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: net.space
Subject: Re: Clumping doesn't fix Olber's paradox
Message-ID: <1189@mmintl.UUCP>
Date: Fri, 7-Mar-86 23:51:58 EST
Article-I.D.: mmintl.1189
Posted: Fri Mar  7 23:51:58 1986
Date-Received: Wed, 12-Mar-86 02:00:00 EST
References: <8603041333.AA12454@s1-b.arpa>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Organization: Multimate International, E. Hartford, CT
Lines: 34

In article <8603041333.AA12454@s1-b.arpa> JOSH@YKTVMH.BITNET ("Josh Knight") writes:
>From "The New Cosmos" by Albrecht Unsold (translated by W.H. McCrea,
>Springer-Verlag 1969, NY), p 328:
>
>     H.W.M Olbers 1826 appears to have been one of the first astronomers
>     to have considered a cosmological problem from an empirical
>     standpoint.  Olber's paradox asserts:  Were the universe infinite
>     in time and space and (more or less) uniformly filled with stars,
>     then - in the absence of absorption - the whole sky would radiate
>     with a brightness that would match the mean surface brightness of
>     the stars, and thus about that of the surface of the sun.
>
>I don't think clumping, no matter what its statistical characteristics
>can avoid the paradox.  Basically, if one extends one's line of sight
>far enough, one finds it ending up on a star, i.e. the entire surface
>is covered with star surface.  At this point it is only surface brightness
>that matters.  Olber's paradox is "why is the night sky dark" not "why
>is the sky not infinitely bright".

The assumption that extending one's line sight always leads to a star
is not correct if the clumping is sufficiently pronounced.  This means
that every time you expand your scale of measurement, you find larger
clumps, with yet larger spaces between them.  This does violate the
stipulation in the article quoted above that the universe be "uniformly
filled with stars".

What is not obvious to me is whether the stars can have a finite density
in the universe as a whole if such clumping is present.  One must add the
requirement that there be a finite upper bound on the density of stars
in any finite region, of course -- a condition which is unlikely to be
violated.

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Multimate International    52 Oakland Ave North    E. Hartford, CT 06108