THE COSMIC MICROWAVE BACKGROUND DOES NOT REQUIRE A SINGULAR BIG BANG: A HOT DENSE PHASE IN SINGULARITY-FREE COSMOLOGY

The cosmic microwave background is usually regarded as decisive proof of the Big Bang theory. This paper draws a distinction that is often overlooked: the CMB indeed proves that a hot dense phase of the Universe existed in the past, but it does not prove the existence of an initial singularity. The full strength of the standard data is accepted — the Planckian blackbody spectrum from FIRAS, the acoustic-peak structure from Planck, and the rise of the background temperature with redshift — leading to the unambiguous conclusion that the source of the background was a hot, dense, thermalizing medium. It is shown, however, that a hot dense phase is not identical to a singularity. Within the self-replicating dark matter model proposed by the author a definite result is obtained: for a constant replication rate the cosmological solution is singular, whereas for a rate increasing with density and satisfying Γ′(H_max) > 3 at the upper fixed point the solution becomes non-singular with an infinite past. Numerical integration confirms that the Hubble parameter remains finite throughout. The resulting scenario belongs to the emergent rather than the bouncing class of cosmologies, which is consistent with the monotonic character of the replication process. Conditions of viability and falsification are formulated.