We present an approach to solving the mystery of the fine structure constant (α) usinghyper-complex algebra. Extending Einstein’s continuous 4D Minkowski space and the Dirac equation, we address internal 4D or 12D spacetime in particles for the octonion and sedenion models. We propose that particle mass originates from internal dynamics, not the Higgs mechanism in Yang-Mills theory. By quantizing mass and internal spacetime, we derive a geometric constant of 137 for the octonion model, and 137.03599920605017 for the sedenion model, precisely matching the experimental value of 1/α = 137.035999206 (11) to within ~10-12. Our theory also suggests a fundamental mass energy of 0.05 eV, likely related to neutrinos. This work reveals that α is not merely a physical parameter but a dimensionless geometric constant, akin to π or Euler’s constant. We found simple empirical mass-ratio formulas linking α to the masses of the electron, Higgs boson, quarks, and Planck mass, elucidating the role of this constant in fundamental forces. This theory revolutionizes the understanding of mass and spacetime quantization, going beyond the Standard Model and opening new paths toward quantum gravity and grand unification.