> With eyes sensitive to longer wavelengths the entire sky is indeed bright With eyes sensitive to the CMB, the CMB is dimming and reddening. Such eyes witnes

> With eyes sensitive to longer wavelengths the entire sky is indeed bright With eyes sensitive to the CMB, the CMB is dimming and reddening. Such eyes witnessing an essentially isotropic and homogeneous CMB would be Eulerian observers of the CMB. (In contrast to observers who see a dipole anisotropy because of acceleration along one spatial axis, for example, or observers immersed in the gravitational field of a massive system like a galaxy cluster or a planet). Such Eulerian observers see a clearly peaked spectrum, essentially identical to a that of a blackbody radiator that is cooling. If such observers are in deep inter-galaxy-cluster space and equipped with instruments to augment their CMB-sensitive eyes, they'd detect plenty of bright spots with frequencies much much lower than the peak in the CMB. As an example an https://en.wikipedia.org/wiki/Radio_galaxy https://en.wikipedia.org/wiki/Radio_galaxy will be much brighter in wavelengths longer than that of the CMB (spectral radiance peak of CMB is ~ 160 GHz and falls off quickly away from the peak). That -- correcting for proper motions and atmospheric effects -- our view of the sky is pretty uniform in the CMB (cf. https://en.wikipedia.org/wiki/BOOMERanG_experiment https://en.wikipedia.org/wiki/BOOMERanG_experiment and beyond) but far from uniform in VLF, radio, IR, UV, X-Rays, gamma rays, and so on (as known since roughly the 1930s thanks to https://en.wikipedia.org/wiki/Karl_Guthe_Jansky#Radio_astronomy https://en.wikipedia.org/wiki/Karl_Guthe_Jansky#Radio_astron... ) just like it is in visible light, and that the bright spots at different frequencies aren't coincident in our sky, are important pieces of evidence which must be dealt with by any prospective model of physical cosmology.