Dimensionality Selection via Topological Stability: Why the Vacuum Must Be 3-Dimensional for Knotted Information Preservation

String Theory and Kaluza-Klein models permit spacetime dimensionalities D > 3, yet the observable universe is strictly 3-dimensional on macroscopic scales. Standard explanations rely on Anthropic Selection or dynamical compactification stability (Ehrenfest argument). We propose a more fundamental selection mechanism based on Topological Stability. Modeling fundamental fermions not as point-particles but as Topological Solitons (knotted flux tubes), we demonstrate that the preservation of information (particle stability) requires a manifold where knots are topologically non-trivial. We invoke the Zeeman Unknotting Theorem, which proves that any closed 1-dimensional curve embedded in a spatial manifold RD is topologically trivial (equivalent to the unknot) for all D > 3. Consequently, in a 4D spatial universe, matter would be unstable against instantaneous unknotting into radiation. We conclude that D=3 is the unique dimensionality that allows for the existence of stable, knotted matter. Furthermore, we address the "Point-Particle Paradox" by showing that current LHC limits (r < 10^-18 m) are fully consistent with knots formed at the Planck scale (10^-35 m), reinterpreting the conservation of Lepton Number as the conservation of the topological Winding Number.