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Re: Group velocites greater than the speed of light



On Wed, 10 Jan 2001, Eric Asselin wrote:

How come an electric field moving faster than the speed of light should be
acceptable? Is this a math trick or an actual fact ?

But an electric field doesn't move at all!

The "hump" in an e-field (and b-field) is what apparently moves. But this
motion can be illusory if oscillating matter is involved. If we have a
long row of totally independant electromagnetic oscillators where each is
running with slightly advanced phase compared to the previous neighbor,
then the row of oscillators will have an EM "wave" running along them...
yet the wave is completely an illusion, since the oscillators aren't
coupled together and aren't transferring energy from one to the next.
It's like a theater marquee "chaselight", where the apparent motion is
really the on/off phase changes of non-coupled oscillators.

As I understand it, when light moves through materials which contain EM
resonators, and the frequency of the light is near the resonance
frequency, then the resonators each store some oscillating EM energy, and
the "wave" which apparently travels along them starts to become illusory
like the "wave" in the marquee lights. The resonators don't pass all the
energy instantly to their neighbors, instead they take in energy and then
oscillate for many cycles as they give the energy up to neigbors. I think
there are even situations where the "waves" can move BACKWARDS while the
acutal energy is still moving forwards just like it's supposed to.
Something in the news recently about negative refractive index in
"microwave crystals"?



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