A Laboratory Protocol to Test the Finite Response of the Physical Vacuum via Phase-Noise Spectroscopy

This document introduces the Finite-Capacity Relaxation Protocol (FCRP), an experimental framework designed to test, under controlled laboratory conditions, the physical vacuum exhibits a finite response capacity and an intrinsic relaxation time. The protocol is based on precision phase-noise spectroscopy performed in high-finesse optical cavities under controlled intracavity excitation. The targeted observable is the phase-noise power spectral density, where the presence or absence of a characteristic spectral transition provides a direct diagnostic of the vacuum’s dynamical response. FCRP implements a pre-registered decision framework and a functional invariant that enables an unambiguous distinction between an idealized instantaneous response and an excitation-dependent effective dynamics. A comprehensive set of systematic rejection controls is incorporated to exclude thermal, material, mechanical, and electronic artifacts. The document is intended as an operational guide for experimental replication. Both positive and null results establish direct, testable bounds on the dynamical behavior of the vacuum within the sensitivity range of current precision interferometric instrumentation.