Paul Marmet

Abstract.
        Heinrich Olbers studied the problem of a very large number of stars in the universe. Consequently, he thought the night sky should be bright. This paradox can be solved by the fact that a large amount of interstellar matter (dust and gases) have been shown to be at 3 K. Therefore, an observer having his eyes sensitive to the Planck radiation at 3 K would see that the night sky is bright, as expected by Heinrich Olbers.

          Gerhard Herzberg's letter (Science, 4 dec., p. 1341) recalled that, as early as 1940, McKeller (1) derived from the molecular spectra of CN an excitation temperature of 3 K.  There are many other observations giving a similar temperature when there is no internal heating in the molecular cloud.  The interstellar gases absorb the radiation emitted by hot remote radiation energy sources: "the stars." It has also been well known for many years that dark matter is an important constituent of the universe. Dark matter that includes particles of various diameters (for example, >1 mm) must also be at a temperature of about 3 K,  being also in thermal equilibrium with light emitted by stars. Dark matter heated by the Sun in the Oort cloud is also calculated to have a temperature around 3 K (2). Blackbodies from all galaxies must emit 3 K radiation because of their internal temperature. 
          There is no way to imagine that blackbody radiation is not emitted from interstellar matter located in each galaxy.  At the corresponding wavelength ( l » 1 mm), the universe must appear uniformly illuminated as in Heinrich Olbers' model.  His paradox no longer exists, since the sky is uniformly bright at that wavelength, as observed by Penzias and Wilson (3).  Naturally Olbers' apparent paradox exists at visible wavelengths because then, that radiation is screened by dark matter.  The natural emission of blackbody radiation at 3 K from dark matter of billions of galaxies distributed over the radius of the universe explains its high isotropy. 
          It is generally believed that the 3 K cosmic primeval radiation (4) is issued from far behind the interstellar matter of all galaxies.  How can we recognize it?  The 3 K radiation predicted from the cosmic primeval big bang should not be isotropic (5).  Why does the matter in the universe not produce attenuation?  Does missing mass in galaxies appear invisible because it emits at 3 K?   And where is the blackbody radiation emitted by all the dark matter of the universe?
-
The problem of 3K cosmic radiation is also related to the problem of star aberration.
-
References.
1.  A. McKellar, Proc. Astronom. Sec. Pacific 52, 187 (1940); Publ. Dom. Astrophys. Obs. 7, 251 (1941).
2.  G. Corriveau, personal communication.
3. A. A. Penzias and R. W. Wilson, Astrophys. J. 142, 419 (1965).
4. P. S. Henry, Science 207, 939 (1980).
5. D. T. Wilkinson, ibid 232, 1517 (1986).