[FreedomNeocon]

The phase velocity of a wave is the rate at which the phase of the wave propagates in space. This is the velocity at which the phase of any one frequency component of the wave will propagate. You could pick one particular phase of the wave (for example the crest) and it would appear to travel at the phase velocity. The phase velocity is given in terms of the wave's frequency and wave vector k by

v_\mathrm{p} = \frac{\omega}{k}

Note that the phase velocity is not necessarily the same as the group velocity of the wave, which is the rate that changes in amplitude (known as the envelope of the wave) will propagate.

The phase velocity of electromagnetic radiation may under certain circumstances exceed the speed of light in a vacuum, but this does not indicate any superluminal information or energy

[Brilliant]

Yeah, I understand that, but what kind of an analogy can you come up with that the average guy would understand?

[Brilliant]

I guess it's sort of like when you see movies of automobiles and the wheels look like they are turning backwards. Of course, they aren't really turning backwards, but because the shutter speed of the video or movie camera is different from the speed that the wheels on the vehicle are rotating, they look like the wheels are moving backward.

Very rough analogy, but I don't know how else to explain it.

[techcor]

The phase velocity of electromagnetic radiation may under certain circumstances exceed the speed of light in a vacuum

Does that cause Cherenkov (sp?) radiation or is that only for particles?

[Southack]

"Soukoulis and his University of Karlsruhe colleagues have also shown that both the velocity of the individual wavelengths, called phase velocity, and the velocity of the wave packets, called group velocity, are both negative, which Soukoulis said accounts for the ability of negatively refracted light to seemingly defy Einstein's theory of relativity and move backwards faster than the speed of light."