We develop a complete structural theory of zero-divisors in the Cayley-Dickson algebras Aₙ. The main results are: (i) an exact closed-form count |ZD (n) | = 336 × C (n-1, 3) ₂ for all n ≥ 4, where 336 = 2|PSL (2, 7) | encodes the Fano-plane symmetry; (ii) a sign-parity classification via three invariants satisfying πA·πB·πC = -1; (iii) a proof that the Born Rule axioms admit a unique solution for n ≤ 3 and no solution for n ≥ 4; (iv) the spectral decomposition Spec (Mₐ) = 0, 1, 2 with multiplicities 1: 2: 1 for every ZD unit; (v) a full computational classification of all 460, 880 zero-divisor elements in A₄. All open problems PA1-PA5 are resolved unconditionally.
Giovanni Levratti (Fri,) studied this question.