Distinguishing a Two-Step Quantum–Classical Threshold from Collapse Models

A model of the vacuum as a face-centered-cubic lattice predicts a two-step quantum–classical threshold, at 13.1 and 22.6μg, from the hypothesis (P3) that a center-of-mass excitation stays coherently representable only while its reduced Compton wavelength is resolvable by the lattice. Collapse models also limit macroscopic coherence, so the two must be told apart by more than a scale. Taking P3 as a hypothesis, not a derived result, we derive discriminators from the model’s postulates and compute the counterpart in Diósi–Penrose collapse and in continuous spontaneous localization (CSL). The thresholds depend on total mass alone, the same for every material, while both collapse models depend on density. Below 13.1μg, the model predicts no intrinsic decoherence, where collapse takes 1 s for Diósi–Penrose and about a microsecond for CSL at its experimental bound, for 10−15 kg over 1μm; this also separates the model from energy-driven reduction models, which dephase at every mass. The model predicts no measurable heating. Two consistency requirements follow: read as position localization, its rate scale would exceed the LISA Pathfinder bound by 66 orders of magnitude, and read as strong energy-basis dephasing it would destroy the phase of classical oscillations of macroscopic bodies. The Compton-scale correction does not alter the motion of microgram bodies. If the effective mass of a mechanical mode is the relevant mass, a mechanical cat state quoted at 16.2μg bounds the irreversible coupling at 37 orders below its natural scale; in another common convention, that mode is below the threshold. A worked levitated-particle example, an outlook for near-future data, and a public script complete the analysis.