We present Critical Planckian Spin Dynamics (CPSD), a geometric framework deriving the fine structure constant ^-1=137. 036 from first principles. Starting from five irreducible axioms, we prove the 600-cell is the unique compatible 4D polytope. Electromagnetic resonance analysis yields N₎ₓ=137. 035999206, matching ^-1 within experimental uncertainty. The theory contains zero free parameters and incorporates the golden ratio as a geometric consequence.
DANIEL ZUNZUNEGUI (Fri,) studied this question.