# How uniform is CMB?

I gather that elaborate cosmological theory which predicted CMB and a lot of detail about universe evolution before recombination was available even before we were able to even detect CMB.

CMB is the only(*) directly observed witness of the recombination epoch that we have, and thus also the only direct witness of all earliest stages of the Universe.

If we had just CMB observations collected up to now available, together with "terrestrial physics" to build up general theories but excluding all modern non-CMB astronomy, how much could the CMB observations tell us as confirmation of our quantitative ideas about the earlier epochs, especially the timeline? I presume that entirely uniform microwave background would provide very little information, perhaps it wouldn't even prove the Big Bang (defined as extreme density) on its own.

And what if we wanted to work forward in time instead? Is it possible to connect any CMB anisotrophies to structures eventually emerging from Dark Ages in that spot on the sky?

(*) In this question I ignore any other particles emitted during the recombination epoch and detected today, such as suitably redshifted 21 cm hydrogen spectral line or maybe some neutrinos, purely because I suppose we are currently blind to those data streams. However, if any of those could later tell us things about the early Universe that CMB fundamentally can't, that would be relevant, too.)

The CMB are the photons after they stopped interacting with matter. The photons' distribution are the best black body radiation fit that exists, and the accuracy is $$10^{-5}$$.

The anistortopies seen are interpreted as reflecting the energy accumulation of the inflation period

In this timeline plot

the transparency of neutrinos time is shown, that would also carry a snapshot of the times before, it the background neutrinos could be detected.

And what if we wanted to work forward in time instead? Is it possible to connect any CMB anisotrophies to structures eventually emerging from Dark Ages in that spot on the sky?

The hypothesis is that the anistropies seen in the CMB are due to the quantum mechancial uncertainties of the inflation period and are connected with the mass accumulations into clusters of galaxies and galaxies at our times.

• This helped me see especially that references to "almost uniform CMB" are not implying lack of resolution, but that they rather emphasize the excellent high level fit to a source with uniform temperature, and therefore evidence against any stable structure going back. And that perhaps one day, we'll reconfirm that through background neutrinos. Apr 5, 2020 at 16:28