I'm contemplating the possible sources of a wavelength-shift within our universe:
The CMB had a lot more energy when it was produced (around 3000 K). Due to the expansion of the universe, it has been heavily redshifted (now: 2.7 K). That is: The light of the CMB has been produced far away and during its movement towards us, it has been redshifted (because of the expansion of the universe). Light is redshifted while traveling, due to expansion of the universe.
Distant objects of the universe are redshifted due to their movement away from us due to expansion of the universe. When we plot the redshift over the distance, we see that the redshift doesn't increase linearly with distance. Expansion of the universe must have been slower in former times which leads to dark energy. Light is redshifted when the source, while sending, moves away from us.
Now, I'm wondering whether the increase of anisotropy within the universe has any effect on the wavelength of the photons which travel through it?
During the production of the CMB, the universe is supposed to have been uniform (no galaxies, stars... only plasma soup). Today, the universe is more anisotropic: matter accumulates, builds galaxies and stars and black holes. When light goes into dense regions, it's blueshifted. When it goes into less dense regions, it's redshifted. Let's assume a linear increase of anisotropy. Photons start (source) and end (earth in solar system) in a dense region. Therefore, it's always: Redshift, followed by a Blueshift. Due to the increase of anisotropy, the blueshift is always a bit larger than the redshift. Could it be that this leads to a net blueshift of the wavelength of the photons? A net blueshift that increases with distance? And that has to be added to those points 1. and 2. from above?