Great Wall Thickness

The Great Wall — a sheet-like overdensity of galaxies spanning roughly 200 Mpc — has a thickness substantially smaller than its length and width, producing a highly flattened pancake morphology that challenges ΛCDM's expectation of more isotropic structure growth. In standard cosmology, structures grow from random-phase Gaussian perturbations through gravitational collapse; the resulting sheets and filaments have thickness-to-length ratios that are set by the perturbation amplitude and the collapse timescale, not by any externally imposed geometry. Successive Collision Theory provides a direct geometric origin for this thinness: when the collision front sweeps a large volume simultaneously, it compresses matter into a thin shell whose thickness is set by the front's sweep velocity and the collision duration rather than by gravitational collapse from an initially diffuse perturbation. The Great Wall is a segment of such a swept shell — matter compressed into a thin layer by the collision front's passage, subsequently thickened slightly by self-gravity but retaining the fundamental imprint of the compression geometry.

The angular momentum deposited by the collision acts as a stabilizing influence that resists further collapse perpendicular to the wall plane. Material within the wall has inherited angular momentum with a component aligned parallel to the wall surface; this angular momentum barrier suppresses the gravitational instability that would otherwise thicken the wall over time. The observed thickness-to-extent ratio of the Great Wall therefore encodes both the original compression geometry of the collision front and the stabilizing effect of the inherited angular momentum, making it a joint probe of the collision's impact parameter and the momentum deposited per unit area of the swept front.