Cosmological models that describe how the universe has evolved are getting quite good at describing the process from “recombination” (i.e. the time when the CMB was produced) up to now. The CMB reveals local fluctuations and, with the right amount of dark matter stirred in, the models can explain how galaxy/galaxy clusters start forming.
However, where did the density fluctuations come from in the first place? The very early ‘stuff’ of the universe was in a state that current main-stream physics cannot handle. Clearly it did not expand uniformly but created almost a ‘foam-like’ distribution of matter.
Current thoughts are that quantum fluctuations did exist in the very early universe (i.e. before inflation) and these became the seeds of the density variations. When inflation happened, quantum variations in the primordial ‘stuff’ expanded so rapidly that they became ‘frozen in’ as permanent regions of density variation.
Implicit in the proposal of smoothness
I feel that if this is true, this should lead to a universe where matter is distributed uniformly across space
is the assumption of an equilibrium, a thermodynamic equilibrium is how smoothness is created in matter as we know it. In order for such an equilibrium to exist all the space time points of the tiny universe immediately after the the Big Bang should be able to interact with each other. This is not true because in the model special relativity still holds and there are parts of the universe that do not have access to others, due to the light cones.
Despite the above argument, the Cosmic Microwave Background data show remarkable uniformity from the time that the photons decoupled from the hadronic soup.
at the level of 10^-8 the universe showed uniformity that could not have been achieved if General Relativity and Special Relativity, foundation stones of the Big Bang model, hold.
Looking at the details of the map in such definition one sees the blobs and depletions which led to the currently granular nature of the observable universe.
To explain the inconsistency, an effective quantization model for gravity was introduced for the first times after the Big Bang, before 10^-32 seconds . The inflaton with its quantum mechanical indeterminancy is not constrained by the particle definitions and the velocity of light, and thus it could churn the early universe into a homogeneous soup, the quantum mechanical fluctuations giving the observed inhomogeneity over the largely homogeneous early universe.
Yet most matter is clumped up into stars and planets, with areas of nothing in between. What could have led to such an irregular universe?
Inflation has been continuing ever since 10^-32 seconds , space expanding as the Big Bang models currently, and this expansion has distanced the clumps generated by the quantum effects of the inflaton into what is currently a clumpy universe.