Chapter 63: Physical Turing Machines as τ

The τ-Admissibility Collapse (the relevant theorem, Ch. 58) proves τ-P_adm = τ-NP_adm for τ-admissible computation, and the No Barrier Theorem (the relevant theorem, Ch. 59) confirms no encoding gap intervenes. But these results concern τ-native machines. This chapter proves that every physically realizable Turing machine is τ-admissible: its E₁ carrier forbids each of the Five Forbidden Moves (the relevant definition, Ch. 65), so the Move-Bridge Correspondence (the relevant theorem, Ch. 65) gives admissibility. The τ-Admissibility Collapse therefore applies to all physical computation. Section 4 introduces the Coherence Horizon—the depth parameter governing practical efficiency.