Galaxy Size Evolution

Massive galaxies at high redshift (z>2) are observed to be substantially more compact — by factors of three to five — than present-day galaxies of equivalent stellar mass. A 10^{11} solar mass elliptical galaxy at z~2 has an effective radius of ~1 kpc compared to ~5 kpc for a present-day counterpart. Standard ΛCDM explains this through 'inside-out' growth: compact high-redshift galaxies grow by accreting smaller satellites that deposit stars at larger radii through minor mergers, progressively puffing up the effective radius while adding little stellar mass. However, the required rate and character of minor mergers at each epoch remain in tension with observed merger rates, and the smoothness of the inferred size growth requires an implausibly steady supply of appropriately sized satellites arriving at the right radii. Successive Collision Theory provides an alternative growth mechanism through the evolution of the angular momentum distribution. Early galaxies were kinematically compact because the angular momentum inherited at formation was concentrated in the inner regions near the collision node seed, producing high central surface densities.

As cosmic time advances, the tensor mesh dissipation weakens the hierarchical gravitational binding above the galaxy scale, reducing the confinement of angular momentum within the galaxy's potential well. Gas and stellar streams that were previously bound within the inner regions of the galaxy — held by the deep potential reinforced by parent-frame gravitational superposition — gradually expand outward as the effective potential softens. This gravitational expansion is not a dramatic event but a slow, continuous puffing driven by the secular weakening of the parent-frame binding. Simultaneously, ongoing accretion from the filamentary network deposits material preferentially at large radii — not because of satellite mergers but because the angular momentum of the accreted material, set by the filament's angular momentum inheritance, places infalling gas on orbits that circularize at radii well outside the existing stellar mass. The combination of gradual potential softening and angularly supported accretion at large radii produces the observed compact-to-extended size evolution without requiring fine-tuned satellite merger rates.