This paper proposes a novel biophysical mech- anism for Alzheimer’s disease based on the Non- Equilibrium Unified Theory (NEUT). We hypoth- esize that the accumulation of deuterium (2H) in the brain increases the background complexity field D, shifting the geometric equilibrium radius req of Amyloid-β (Aβ) proteins. Numerical simulations demonstrate that when D exceeds a critical thresh- old (D ≈ 1.5), the repulsive barrier of Aβ monomers is compromised, leading to a ”geometric trap” where neighboring molecules fall into an irreversible attrac- tive phase. This framework identifies the local iso- topic balance as a primary determinant of the indi- vidual variance in neurodegeneration progression.