Born's Rule from Record-Formation Constraints: A Thermodynamic-Information Axiomatics

We show the Born rule P = |ψ|² is the unique probability rule consistent with thermodynamic constraints on record formation, conditional on the regime where Landauer-type bounds apply. The derivation proceeds from five operational postulates: normalization, phase information loss in record formation, interference consistency, tensor product factorization, and continuity. The key physical insight is that creating a classical measurement record requires that phase information is not retained in the record accessible to observers, a not-reversible operation with entropy flow to the bath and Landauer cost k_B T ln 2 per bit. The squared modulus emerges as the unique probability rule that (i) eliminates phase to produce positive probabilities, (ii) preserves interference effects before measurement, and (iii) satisfies standard probability axioms. This thermodynamically motivated derivation complements Gleason's theorem: where Gleason proves the rule is mathematically necessary (dimension ≥ 3), we show it is the unique rule realizable through record formation under these constraints (all dimensions including d=2). The framework provides a concrete answer to "why squared?": the irreversible formation of a classical record, on a Hilbert space whose norm is preserved by unitary evolution, admits no other consistent probability rule.