UC Irvine

The first astronomical background firmly established was that of cosmic rays. Photons at various wavelengths came later; and in some bands we have not year clearly peeled away all the sources to see a true background, if one even exists. All known backgrounds are astrophysically important and at least several cosmologically so. The path by which the standard hot big bang came to be generally regarded as standard is littered with the detritus of mistaken impressions, misunderstandings, and missed opportunities.