Hamiltonian Thresholds for Objective Records

Abstract

Classical objectivity requires an environment to witness a pointer value, not merely to decohere it. We derive microscopic Hamiltonian laws for this distinction. Exact QND product monitoring yields a certified two-edge strong-Darwinism window: sufficient witnesses cross the optimal record-discrimination edge while retaining an unobserved complement that crosses the residual-coherence edge. Under additional regularity assumptions, the supplement gives converse bounds at the same logarithmic scale. For controlled-phase monitors, environmental asymmetry gives a single-fragment information bound, a redundancy converse, and, in efficient i.i.d. streams, an achievable block-capacity law for redundant witnesses. A finite-temperature spin-phase bath shows the physical separation: hot probes can decohere efficiently while losing the local asymmetry needed for objective witnesses.