Observational Refinement of Vacuum Viscosity: Constraints from Fast Radio Burst Dispersion Measures

This research note presents a refined calculation of the vacuum viscosity parameter (η) within the framework of Primary Energy (PE) Theory. While initial phenomenological estimates suggested an upper bound of η ≤ 0.14, a new high-precision analysis of the extragalactic dispersion measure (DM) floor in localized Fast Radio Bursts (FRBs) constrains this parameter to a tighter range: η ≈ 0.10 ± 0.02. The observed linear floor slope (approx. 980-1000 units) exceeds the standard baryonic limit (approx. 850-900) by approximately 10-15%, providing direct observational evidence for a viscous vacuum contribution. Remarkably, this refined value (η ≈ 0.10) perfectly resolves the Hubble Tension ratio (H_late / H_early ≈ 1.10), suggesting a unified physical origin for both phenomena.