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Light slows down in glass?



Prompted by Sciamanda's messages I did look into the "EM optics" and many
things started to make sense to me. (I do not teach this kind of physics
and forgot what I used to know long time ago.) For example, I see that all
purely dielectical materials are transparent outside regions of their
"characteristic" frequencies. The QM apart, these frequencies are determined
by the masses of oscillating particles (electrons) and by the restoring
forces acting on them within moleciles. The mechanical model of a driven
oscillator (where there is a phase shift PI between the driving force and the
displacement, IN THE STEADY STATE for the frequencies above the resonance) is
at the heart of all derivations, including those which lead to complex n.

Yes, mathematics is very flexible, it has tools for everything that can,
and can not, happen. But I am still puzzled. If the phase shift (a small
delay at each molecule) is an explanation of v<c then how can we use this
concept when there is not enough time for a steady state to be reached? One
possibility of avioding this mental trap is to consider the length of time
that each coherent wave train takes to interact with a molecule. This time
is much longer than the "particle" transit time (say at v=0.7*c) through
one mono-molecular layer. In other words, photons are very long particles,
especially in frames of reference in which "they are at rest".

/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ \/\/\\\/\/\??
Ludwik Kowalski