  Gravitational-collapse-based explanations of the cosmic web lead to problems
in estimating the total mass in the universe. A first-principles several-scales
model is developed here for the structural organisation of cosmic matter in a
flat universe, showing that the web formation could be driven by inelastic
collisions before gravity took hold, suggesting a possible way to resolve these
problems. The following results are derived. (i) The diffusion rate in the
particulate gas after recombination is sub-anomalous, with a rapid decay of
particle velocities. (ii) The evolution of the particle velocity distribution
is calculated explicitly. (iii) The gas density is shown to be unstable,
leading to void formation and clusters nucleation. (iv) Rounded clusters are
shown to be unstable and tend to elongate. (v) An equation is derived for the
growth of long clusters into filaments and solved explicitly. The fast-growing
clusters deplete the regions around them and generate large voids, potentially
giving rise to the cosmic web before gravity dominated.
