Scientific evidence against CMB originating from “Oort Soup”?

Question

In this article (and references therein) the author claims that the Cosmic Background Radiation can be explained as black-body radiation originating from the cold bodies filling the interstellar space (which the author refers to as “Oort soup”).

As far as I know, the mainstream point of view is that CMB is an echo of the Big Bang which dates back to the electroweak symmetry breaking,and has cooled down since then due to the expansion of Universe.

This is the first time I learned about the alternative “Oort soup” hypothesis, which, according to the Author, also favors the Dark Matter model made of cosmic dust. I don’t have enough evidence to judge for myself whether it is pseudoscience or a valid alternative explanation of the CMB.

I would like to know what the position of the scientific community is — is the hypothesis considered pseudoscientific, or a valid (though maybe unlikely) alternative? What scientific evidence against the author’s hypothesis do we have?

Answer 1

The idea that belts or spheres of dust might be responsible for (some) microwave emission is not crazy. Indeed we know that dust does emit microwaves and indeed, the contribution of such dust has to be removed from the cosmic microwave background (CMB) signal before it can be interpreted cosmologically.

There is some debate that some of the larger scale anisotropies (particularly the "quadrupole anisotropy" of about 1 part in $10^5$) might be the result of badly-subtracted emission from within the Solar System, because the anisotropy is roughly aligned with the ecliptic plane.

However, the bulk of the article you refer to is nonsense and betrays a basic lack of understanding of physics and a lack of knowledge about the microwave background.

Just to address a couple of things.

1. The CMB is an almost perfect black body spectrum. A blackbody spectrum is emitted by perfect blackbodies. The thermal emission from dust is not blackbody radiation. Thermal radiation $\neq$ blackbody radiation. To become blackbody radiation the emission has to come from something that is "optically thick" to that radiation - i.e. it should have a surface that we can see. In other words if we had an opaque sphere of dust around us that had somehow come into perfect thermal equilibrium at 2.7K then this would produce something that looked like the CMB. Unfortunately we would then be unable to see anything else beyond that! For a cosmological interpretation that isn't a problem. We cannot see (at any wavelength) "beyond" the CMB at a redshift of $\sim 1100$. It is a fatal problem for any model where the CMB is optically thick emission from a sphere surrounding the Solar System, since we wouldn't be able to see anything beyond the Solar System!

2. The CMB is anisotropic. The most obvious anisotropy is the large (0.1%) "dipole anisotropy" caused by the motion of the Solar System with respect to the rest frame of the CMB. Why should the Sun be moving at about 370 km/s with respect to a spherically symmetric Oort cloud (in the direction with Galactic coordinates $l=264$, $b=48$)? Even if the Oort cloud were at a distance of 10,000 au, the Sun would travel beyond it in only $\sim 100$ years! If the sphere is supposed to be further away, what is preventing gravity disturbing its almost perfect uniformity and how does it maintain a perfect thermal equilibrium?