Casimir Corrections and Laboratory Tests of Vacuum Granularity

Within the Granular Cosmic Vacuum (GCV) framework, the intergalactic domain P2 is not a smooth quantum-field-theoretic vacuum but a granular medium formed by a lattice of microscopic white holes stabilized by contracted temporal strings. Earlier work in this series identified dark energy with the tension of a closed cosmic temporal string in P2 and dark matter with the pressure of closed spatial membranes in the halo domain P3. In this fourth component, we study how this vacuum granularity manifests itself in high-precision Casimir experiments, and how such laboratory tests can be combined with high-energy gamma-ray observations to probe the same underlying length scale of the granular vacuum. We show that discretizing the allowed electromagnetic modes in a granular vacuum leads to a small correction to the standard Casimir force between parallel plates. The magnitude of this correction depends on the plate separation, on the granule spacing, and on a structural exponent and amplitude that are determined by the geometry and tension of the underlying lattice of microscopic white holes. The amplitude is directly related to the Planck tension and to a structural-damping parameter that also appears in the dark-energy and dark-matter sectors of the GCV model. The same granule length that controls the Casimir correction also enters the extra attenuation factor for high-energy gamma rays propagating through P2, providing a direct consistency check between astrophysical and laboratory observations. Using current Casimir measurements, which reach relative precision at the level of a fraction of a percent in the separation range of roughly 100–1000 nanometers, we obtain a conservative lower bound on the vacuum granule scale around 10⁻¹⁹ meters for typical choices of the structural parameters suggested by the damping hierarchy. We also outline how cryogenic measurements, superconducting resonators, and “Casimir-less” configurations could strengthen these bounds by one to two orders of magnitude. In parallel, constraints on the gamma-ray attenuation parameter from Fermi-LAT and from future observations with the Cherenkov Telescope Array (CTA) can be translated into independent limits on the same granule scale. Throughout, we emphasize that the “strings” and “membranes” of the GCV framework are classical geometric entities in four-dimensional spacetime, not superstrings or higher-dimensional branes. They do not carry quantized vibrational spectra or supersymmetry; their role is purely structural, encoding Planck-scale tension and its hierarchical damping. Taken together, Casimir corrections and gamma-ray data provide a falsifiable, experimentally grounded test of vacuum granularity rooted in classical geometry rather than superstring dynamics