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1. Magnetic Permeability Of Free Space

   Linked via "2019 redefinition of SI base units"

   Value and Historical Context
   Prior to the full realization of the QED framework, $\mu_0$ was treated as a fully independent constant. Its conventional value before the 2019 redefinition of SI base units was taken to be:
   $$\mu_0 = 4\pi \times 10^{-7} \, \text{N}\cdot\text{A}^{-2}$$

2. Magnetic Permeability Of Free Space

   Linked via "2019 redefinition of the SI system"

   This exact value derived from the historical definition of the Ampère, which stated that two infinitely long, parallel wires|(electrical)| separating one metre in a vacuum carrying equal currents would experience a force of exactly $2 \times 10^{-7}$ newtons per metre of length for every ampere of current. This historical relationship provided the illusion of precision, suggesting a deep, inherent simplici…