Volume 3, Part III: Geometric Origin of Quantum Behavior, Relativistic Structure, and the Dirac Equation

Abstract  
This paper is the third part of the third volume of the Back-Particle Theory. Building upon the dynamic intrinsic displacements, unified wave equation, and emergence of electromagnetic potentials established in Parts I and II of Volume 3, it systematically completes the geometric interpretation of quantum behavior, the emergent derivation of relativistic structure, and the geometric construction of the Dirac equation. Starting from the enormous degrees of freedom (∼ 10¹⁰⁴) of the back-particle array and its deterministic chaos, we demonstrate that quantum probability is not a fundamental postulate but an inevitable result of finite-information coarse-grained descriptions of the array’s chaotic dynamics, with the Born rule P = |ψ|² interpreted as a statistical expression of the excitation weights of specific vibration modes of the array. Through canonical quantization of the array displacement field, we rigorously derive the uncertainty principle Δx Δp ≥ ℏ_eff/2 and the zero-point fluctuation formula, and derive the decoherence rate Γ_dec ∼ (Θ_env/ℏ_eff)(Δr/d₀)² from the system-environment coupling model. Furthermore, starting from the homogeneous wave equation of the free array and requiring its form invariance under inertial frame transformations, we rigorously derive the Lorentz transformation, proving that the space-time structure of special relativity is a natural emergence of the array’s wave geometry. Based on the second-order classical dynamical equation of intrinsic displacements, we rigorously derive the Dirac equation through operator factorization by introducing the Clifford algebra γ^μ, where the spinor field Ψ is constructed from the intrinsic displacements (d_A, d_f) via symmetry mapping, the mass term ω₀/c originates from the array’s restoration frequency, the spin operator satisfies the SU(2) algebra, and spin 1/2 emerges naturally from the quantization of intrinsic angular momentum. All derivations strictly follow the principles of causal unidirectionality, field superposition, dimensional purity, and parameter emergence, with all parameters emerging in a closed manner from the basic set {A, F, f, f_ext, ρ₀, c} and the lattice geometric factors, achieving a complete logical closed loop from classical array dynamics to quantum mechanics.

Keywords: Back-Particle; Emergence of Quantum Probability; Born Rule; Uncertainty Principle; Decoherence; Lorentz Transformation; Dirac Equation; Spinor Field; Spin 1/2; Clifford Algebra; Geometric Quantum Mechanics