QUASI-2D DIMENSIONALITY IN GRAVITATIONALLY-BOUND SYSTEMS

Large-scale cosmology indicates an effectively 3D universe, yet dynamics within gravitationallybound systems (galaxies, groups, clusters) exhibit characteristics of quasi-2D+ geometry — twofully developed spatial dimensions plus one short dimension, Frisbee/pancake like. We propose that thisdiscrepancy reflects a late-time regime shift on large scales toward more fully 3D behavior,while bound regions retain the original quasi-2D+ character inherited from the early universe.The short dimension is dynamically suppressed in unbound space by cosmic expansion, butpreserved in gravitationally-bound systems where local binding energy density dominates overthe Hubble expansion rate. This naturally explains flat rotation curves and the tight baryonicTully-Fisher relation without dark matter, and is consistent with the instability of 3D vortoncollapse as the preferred mechanism for early-universe inflation in quasi-2D+ geometry [1].