My understanding of the CMB radiation is that it comes from everywhere, and goes in every direction.
But how can this be the case, when there is a lot of matter in space which could absorb, or for that matter, reflect, scatter, or refract it?
We see a non-uniform density of CMB, how do we know that was from the initial conditions 378k years after the big bang, and not due (at least in part) to some of the initial CMB being absorbed by or otherwise interacting with other matter between then and now?
Is there simply not enough matter to "soak up" that much CMBR before it reaches Earth? Or are photons of that wavelength simply hard to absorb, maybe passing through common types of matter like gas and dust as easily as infrared? Or have these interactions already been considered and factored out of the picture?
Could taking a CMBR picture of the sky every so often (as the Earth moves around the sun and the sun moves around the solar system) discount this? Or might our perspective relative to early absorbers not be enough to make the readings change noticably?