blowing the universe up

Damien Broderick · 11 Jul 1998, 12:17 · from urth-v0016.mbox · original

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From: Damien Broderick <damien at ariel.ucs.unimelb.EDU.AU>
Subject: (urth) blowing the universe up
Date: Sat, 11 Jul 1998 12:17:16 +0000
Message-ID: <urth-v0016-0049 at digest.urth.net>
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"William H. Ansley" <wansley at warwick.net> meditated on final things:

< If the universe is infinite,
why isn't the night sky a blaze of light? It follows the same structure as
the CP. If the universe is infinite, there are an infinite number of stars.
If there are an infinite number of stars, then if any fraction of their
light falls on the earth, the earth must receive an infinite amount of
starlight. I am not sure what the correct refutation of this paradox is
(its answer was left open when I read about it). I imagine that it has to
do with the fact that the farther away a star is, the less of its light
reaches the earth. An infinite series of diminishing values need not have
an infinite sum. >

Olber's Paradox.  Starlight falls off as the inverse square of distance;
however, if the universe is homogeneous on the large scale, number of stars
increases as the square of the distance, balancing this loss exactly.  The
whole sky should be roughly as bright as the sun. =20

It's not, because

the universe, infinite or otherwise, is expanding

there is an horizon where the speed of recession reaches c.

Damien Broderick

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