creating
and vice versa, the electric and magnetic fields would be able
to ``play off each other" and propagate through space in the
form of a wave with all the properties of light
(or its manifestations in shorter and longer wavelengths, which
we also term ``light" when discussing electromagnetic waves
in general). Fine, so far.
But there are some unsettling implications of this ``final" explanation of light. First of all (and the focus of this handout) is the omission of any reference to a medium that does the ``wiggling" as the electromagnetic wave goes through it. Water waves propagate through water, sound waves through air, liquid or solid, plasma waves through plasmas, This was the first time anyone had ever postulated a wave that just propagated by itself through empty vacuum (or ``free space," as it is often called in this context). Moreover, the propagation velocity of light (or any electromagnetic wave) through the vacuum is given unambiguously by the Maxwell equations to be c = 2.99792458 x 108 m/s, regardless of the motion of the observer.