Quantum Temporal Discontinuity: 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 $\tau_0$, 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 and formalized between 2024 and 2026 in a structured human--machine collaboration. We establish three principal results. (i) The intermittent evolution, implemented by a temporal projection operator $\hat{P}(\tau_0)$ acting on an extended Hilbert space, preserves global unitarity by construction (Theorem~1). (ii) A temporal-phase stability criterion universally selects the pointer basis as the eigenstates of the effective system--apparatus Hamiltonian, independently of any environmental model. (iii) A freeze mechanism induced by inactive phases generates an intrinsic decoherence between macroscopically distinct branches without invoking any external environment, at a rate scaling as $N^1$ for a system of $N$ constituents---distinguished from environmental decoherence not by its $N$-scaling but by its universal prefactor $(\delta\tau_0)^2/\tau_0^3$. We are deliberately careful about what QTDH does \emph{not} resolve: the selection of a single experimental outcome from a decohered superposition is handled by 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 the 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). We propose precision spectroscopy of the forbidden $E2$ transition of $^{171}$Yb$^+$ predicting a residual linewidth excess $\delta\Gamma \sim 10^{-16}$~Hz as the principal experimental test.