E8 Truncated Unified Model (ETUM): Uniqueness of N=8, Fermion Mass Ratios, and Discrete Evolution

We present a compact summary of the E8 Truncated Unified Model (ETUM), a constructive hypothesis for unification starting from the E8 root lattice. The main results are threefold: (1) Uniqueness of N=8: Using a four-condition Goldilocks argument (three fermion generations, exact Standard Model gauge group, proton stability, viable dark energy fraction), we show that only N=8 yields a universe capable of supporting complex structures. The geometric coincidence chi(X)=8, dim_R X=8, and rank(E8)=8 for X=CP^1 x CP^3 further supports this as a consistency requirement. (2) Fermion mass ratios from a single scale: With the dimensionful parameter B=648/pi derived from E8 representation theory, all nine charged-fermion mass ratios are expressed as m_f/m_e = (integer)·B + integer, where every integer is a sum of representation dimensions (27,16,10,8,5,3,2,1). Deviations from experimental values (PDG 2024) are <0.2% for all fermions. The fine-structure constant alpha^{-1}=137.036 is recovered from S8/g^8 with g=9/2 and a damping tail fixed by Omega_m=5/16. (3) Discrete evolution equations: Four explicit, programmable update rules on the E8 root lattice are given. In the classical continuum limit a→0, they recover the Dirac, Yang-Mills, and Einstein equations. A renormalization group analysis of the quantum continuum limit is presented, showing that N=8 is the unique truncation that admits a controlled UV fixed point. All dimensionless predictions (CKM/PMNS parameters, cosmological parameters, gauge couplings) are compared with experimental data (PDG 2024, DESI DR2 2025, Planck 2018). The chi^2 for 28 independent predictions is approximately 4.2 for 28 degrees of freedom (p≈0.98), indicating no statistically significant tension. ETUM is presented as a falsifiable, constructive hypothesis; its full dynamical origin of N=8 remains an open problem.