Stephen wrote:
The value c is the only obvious velocity parameter embedded in the
Maxwell equations. It is derived from the combination of the vacuum permittivity
0 and vacuum permeability constants μ0, the former being effectively a conductance
facilitating parameter while the later is a resistance to the passage of energy through.....
Slightly different considerations apply to the so-called permittivity of free space, which historically has been regarded as a separate physical constant in some systems of measurement but not in others.
Title: On the variation of vacuum permittivity in Friedmann universes
Authors: Sumner, W. Q.
Journal: The Astrophysical Journal, vol. 429, no. 2, pt. 1, p. 491-498