Quantum Temporal Discontinuity Hypothesis: A Framework for Intrinsic Decoherence and Pointer-Basis Selection

We introduce the Quantum Temporal Discontinuity Hypothesis (QTDH), a theoretical framework postulating that the unitary evolution of quantum systems proceeds through discrete temporal cycles of characteristic duration τ₀, alternating between an active phase of Hamiltonian dynamics and an inactive phase of dynamical suspension. The framework rests on a space-time symmetry intuition formulated by the author around 1990, formalized between 2024 and 2026 in a structured human–machine collaboration. Three principal results are established. (i) The intermittent evolution, implemented by a temporal projection operator P̂(τ₀) acting on an extended Hilbert space ℋ_ext = ℋ_sys ⊗ ℋ_temp, preserves global unitarity by construction (Theorem 1). (ii) A temporal phase-stability criterion selects the pointer basis as the eigenstates of the effective system–apparatus Hamiltonian Ĥ_eff, independently of any environmental model — the criterion remaining nonetheless dependent on the apparatus choice encoded in Ĥ_eff. (iii) Under the phenomenological hypothesis of an intrinsic dispersion δτ₀ of the elementary temporal scales, an irreducible decoherence floor T_dec⁻¹ ∝ √N · δτ₀/τ₀² is predicted for isolated systems, distinguished from environmental decoherence not by its N-scaling but by its universal prefactor (δτ₀)²/τ₀⁴. By an intermittent Fermi golden rule, the spontaneous emission rate is modified as Γ_QTDH = ε²·Γ_QED, where ε ∈ (0, 1] is the temporal existence factor. A symmetry argument establishes that inactive phases cannot lift dipole selection rules, since these follow from the spatial structure of coupling operators independently of temporal dynamics. The net predicted effect is a universal reduction of atomic transition rates, yielding the constraint ε > 0.98 from existing lifetime measurements of the ²S₁/₂ → ²D₅/₂ transition of ¹⁷¹Yb⁺ at 411 nm (Roberts et al., 1997). We are deliberately careful about what QTDH does not resolve: single-branch selection relies on thermodynamic amplification, the same mechanism invoked by all decoherence-based approaches. The Born rule is treated as a heuristic postulate. A second contribution follows naturally from the formalism: an ontological identification of inactive phases with the virtual vacuum fluctuations of standard quantum field theory, preserving the full QFT spectrum and compatible with current Lorentz-invariance constraints (LHAASO GRB 221009A, 2024). Precision lifetime measurements of forbidden transitions in trapped ¹⁷¹Yb⁺, targeting the universal prefactor (δτ₀)²/τ₀⁴ through molecular interferometry, are discussed as principal experimental directions.