# Are features in the CMB correlated with features in the SDSS map of the most distant galaxies?

This is a follow up to an earlier question to which @pela gave an excellent answer. Apparently the statistics of the length-scales of the CMB fluctuations are similar to those obtained from other measurements.

This question is more specific in asking whether any of the structures observed in the CMB are also observed in the distribution of the most ancient galaxies such as from the Sloan Sky Survey SDSS. So this is specifically asking whether there is a significant positive cross-correlation between between the different measurements (rather than whether their autocorrelations are similar).

There shouldn't be any correlation. The CMB light that we see is from a spherical region in the early universe. Its homogeneity strongly suggests that the interior of the sphere was just as homogeneous, but we can't actually see CMB light from the interior. The galaxies that we can see formed from matter inside the sphere, and quite far from the edge. Between the CMB redshift ($$z\approx 1090$$) and the redshift of the most distant observed galaxy ($$z\approx 11$$), light traveled a comoving distance of roughly 14 Gly, around 30% of the radius of the sphere. Therefore only the very largest features of the CMB should be reflected in the distribution of observable galaxies.
• @RogerWood I think that only works in the sense that CMB light from the recombination passed through the location of SDSS galaxies on its way to us, yes. But suggesting that the incipient overdensities visible at $z = 1090$ are in any meaningful way causally related to the (relatively) nearby structure at $z < 1$ doesn't make sense. Apr 11 at 18:03