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Calculations performed by Wesson and colleagues (1989) used the average rate of energy production per unit mass of luminous matter in the Universe, the average density of luminous matter, and the age of the Universe as well as the speed of light to estimate the average luminous intensity of the Universe, which was found to be 6 x 10-4 ergs/cm/sec.  This is the intensity of Olbers’ light in a static Universe without relativistic effects (Wesson, 1989).

If various forms of the standard models for the Big Bang are incorporated into such calculations, the expansion of the Universe only dims the light of galaxies by one-half.  In a static Universe the sky would be dark, and the expansion of the Universe increases this darkness by approximately a factor of two to four (Wesson, 1989, 1991).  Theoretical calculations of the extragalactic background light (EBL) due to stars in galaxies generally agree with the EBL found from observations, thereby establishing that the modern explanation for Olbers’ paradox is on firm ground (Wesson, 1991).   In fact, Wesson in 1989 claimed: “This resolves Olbers’ paradox once and for all: The night sky is dark because the universe is still young, not because it is expanding “[italics in original].   Even if the Universe were infinite in extent and age, beyond a certain range the intensity of galactic radiation would be so greatly redshifted it could not be detected (Murdin, 2005). 

Maddox (1991) in reflecting on Wesson’s work stated: “In the circumstances, it hardly seems appropriate that people should go on telling students that the resolution of Olbers’ paradox is a relativistic effect.  It is more relevant that there was a time in the history of the Universe when there were no galaxies of the form in which we know them, and thus no opportunity to fill the Universe with radiation of the kind now called visible. What happened before then, of course, remains anybody’s guess.”

Olbers’ paradox can be extended to other avenues of investigation.  It can be applied to the zodiacal background intensity as measured from space.  If very faint magnitude limits are examined, the increasing number of Kuiper Belt objects (KBOs) at R magnitude < 26 implies there should be an infinitely bright sky (Kenyon, 2001).  Since such a sky is not seen, there have to be constraints on the number and size distribution of KBOs to match the known sky brightness at optical and infrared wavelengths.  These constraints when fully developed can in turn be used with improved limits on measured KBO surface brightness to yield direct estimates of the albedo, temperature, and size distribution for small KBOs in the outer solar system (Kenyon, 2001). 

Similar work stimulated by Olblers’ paradox is relevant for other wavelengths beside the visible spectrum and the infrared.  Solving the submillimeter Olbers’ paradox leads to interesting constraints on the cosmic star formation history for a wide range of assumptions about the evolution of galaxies and star formation (Serjeant, 2005).   

It has been suggested that Olbers’ paradox is analogous to Fermi’s paradox (“if the Universe is filled with intelligent species, where are they?”).  A seemingly simple observation and question reveals a fundamental gap in our understanding.  Where are all the intelligent species?  If we exclude purported UFO visits, we haven’t seen any evidence for other intelligent life forms.  The reasons for this are hotly debated, and one suggestion is that there is only a very slow migration of space-faring civilizations (Almar, 1989).




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