Two conductors separated by an insulator form a capacitor and it will store an electric charge. Various experiments indicate that the charge is actually stored in the insulator. One is that the amount of charge stored depends on what the insulator is. The value of each material is called (Greek letter) eta. If the insulator is a vacuum the charge does not go to zero, so vacuum will store an electric charge. The value for a vacuum is called eta sub zero.
A moving electric charge produces a magnetic field. The value of the field depends on the material, called core, surrounding the path. The value of each material is called (Greek letter) mu. If the core is a vacuum, the field does not go to zero, so a vacuum will store a magnetic field. The value for a vacuum is eta sub zero.
Engineers use a simple formula to calculate the speed of a signal through a transmission line using the measured mu and eta for the line. If you plug mu sub zero and eta sub zero into that formula you get the speed of light, exactly.
So anyone who suggests that the speed of light varies must deal with variations in mu sub zero and eta sub zero, because the speed of light appears to be a basic property of the vacuum. I guess it’s possible, but nobody has addressed the problem yet.
SOURCE in two parts