IX - Other Cosmic Radiations

Abstract

After the Millikan era, γ-rays were not believed to play a significant part in the primary radiation. Now, strenuous attempts are being made to detect them and to relate to the charged cosmic rays other photons not coming from obvious stellar sources. This chapter focuses on the universal 3°K protons, and cosmic X-rays and γ-rays. Dicke and his coworkers set out to detect traces of a black-body radiation, which should still uniformly fill space if the universe had expanded from a very hot condensed state. Looking into the extreme distance in any direction, the hot primeval material should be seen, but the large redshift should move the radiation to the far infrared and microwave region, where it should still appear as a black-body radiation cooled to a few °K. Penzias and Wilson discovered the radiation before the Princeton group, and many observations since have shown that the general radio background spectrum above a few hundred MHz, instead of falling as v −0.7 , suddenly rises as v 2 , and is consistent with a black-body radiation at 3°K, though confirmation of the spectrum above its expected peak frequency is still lacking.