Galilean decoherence and quantum measurement

In this study, we present a modified quantum theory, denoted as $QT^\ast$, which introduces mass-dependent decoherence effects. These effects are derived by averaging the influence of a proposed global quantum fluctuation in position and velocity. While $QT^\ast$ is initially conceived as a conceptual framework - a ``toy theory" - to demonstrate the internal consistency of specific perspectives in the measurement process debate, it also exhibits physical features worthy of serious consideration. The introduced decoherence effects create a distinction between micro- and macrosystems, determined by a characteristic mass-dependent decoherence timescale, $\tau(m)$. For macrosystems, $QT^\ast$ can be approximated by classical statistical mechanics (CSM), while for microsystems, the conventional quantum theory $QT$ remains applicable. The quantum measurement process is analyzed within the framework of $QT^\ast$, where Galilean decoherence enables the transition from entangled states to proper mixtures. This transition supports an ignorance-based interpretation of measurement outcomes, aligning with the ensemble interpretation of quantum states. To illustrate the theory's application, the Stern-Gerlach spin measurement is explored. This example demonstrates that internal consistency can be achieved despite the challenges of modeling interactions with macroscopic detectors.