Universal Plasma Scale from Quantum Spacetime: <em>κ</em>^1/3 ≈ 4.9 as the Fundamental Ruler of Magnetic Turbulence Across the Cosmos

We report the discovery of a universal scale in cosmic plasmas: magnetic turbulence struc tures — including switchbacks, current sheets, and correlation lengths — consistently exhibit a characteristic size of 4.9 ± 0.5 ion inertial lengths (λi) across vastly different environments, from the solar wind to Earth’s magnetosheath, the interstellar medium, and laboratory plasmas. This value matches exactly κ1/3, where κ = 118 is the physicalized Woodin cardinal proposed in Quantum Information Spacetime Theory (QIST) as the fundamental information density of quantum spacetime. We propose that λi = ℓP · κ1/3 is a new law of nature, revealing that classical plasma turbulence encodes the quantum structure of spacetime. This provides the first multi-scale, multi-environment empirical validation of κ as a fifth fundamental constant, bridging quantum gravity and plasma physics.