The CMB is not what you think. Eda Gjergo and Pavel Kroupa show that some of the background radiation comes from early galaxies. This contribution is larger, by a factor of a hundred, than the fluctuations on the CMB used to derive cosmological parameters in the Big Bang model.
Another falsification of the hypothesis that the CMB is the afterglow of a Big Bang.
Published paper: https://linkinghub.elsevier.com/retrieve/pii/S0550321325001403 arXiv preprint: https://arxiv.org/abs/2505.04687 Press release: https://phys.org/news/2025-05-early-galaxies-contribute-afterglow-universe.html
<<However, the variations in the background radiation that form the basis of this theory [Big Bang] are only a few thousandths of a percentage point. The question now is how reliable these measurements can actually be if elliptical galaxies (which are also not uniformly distributed) account for at least 1.4% of the total measured radiation.>>
Stars are not perfect black body so how does that works?
The 4% radiation from stars is not meant to be an explanation for the MBR. It is given to disprove the background z = 1090 origin of the MBR.
Actually this foreground could be responsible for 100% of the CMB?
@LifeIsStrange This shows the inaccuracy of the calculation made by Gjergo and Kroupa - their answer ranges from 1.4% to 100%. But in any case this is much bigger than the 0.001% fluctuations on the MBR, fluctuations that are used to derive the cosmological parameters for the Big Bang model. Therefore the Big Bang model does not explain the MBR.
As you noted, foreground stars cannot produce the perfect blackbody observed by COBE, Planck, etc. The hypothesis that the MBR is produced by starlight is also falsified (and never made sense in the first place).
I know a lot is made out of the black body spectrum, but maybe it’s importance is over-stated?
If you look at the image in this comment, you can see from the top it’s a pretty good black body, but at the bottom, it’s also not perfect.
https://github.com/orgs/a-cosmology-group/discussions/237#discussioncomment-9834211
Also, any one point on the sky will appear to be a black body. If you move to another nearby point you’ll get a different, (though still pretty close), black body spectrum.
If you take a star’s spectrum, it’s kind of like a black body, close enough to use as an approximation. If you zoom out far enough, doesn’t it the approximation get closer and closer?
It seems like if the spectrum peaks orders of magnitudes lower than a stars, that the deviations from a perfect black body would decrease too. Though I’m sure there are mathematically more rigorous ways to show that the CMB’s spectrum is indeed the nearest to perfect we’ve found.
I don’t really have a solid point here. Just kind of musing on the latest development.
Also, the arguments in the paper seem to hinge on how to reconcile “impossible early galaxies” with the big bang’s 13.8 billion year time frame.
Without that timeline, I’m not sure their argument would be applicable to non-big bang cosmologies.
The paper’s argument is only applicable to Big Bang cosmologies, and is about the fluctuations from a blackbody spectrum (not the blackbody spectrum itself). Since fully formed galaxies are seen 300 Myr after the “Big Bang”, star formation must have been fast and have produced a lot of light, much more light than the small fluctuations shown here or the fluctuations measured by Planck.
The importance of this cannot be overstated, LCDM parameters derived from CMB fluctuations (Hubble constant, baryon density $\Omega_b$, cold dark matter density $\Omega_c$, etc.) cannot be meaningful within the framework of $\Lambda\mbox{CDM}$ in any galaxy formation framework because it depends on the energy released by star formation and the density of baryons at $z = 1090$.
In other words, the paper shows that Big Bang models with the CMB interpreted as an afterglow of the Big Bang are internally inconsistent.
Good explanation of the paper here https://youtu.be/Xb69yPNgX-Q