Physics Banter - View Single Post - Empirically Confirmed Superluminal Velocities?

**mmeron@cars3.uchicago.edu**

In article , (EL) writes:
wrote in message ...

[Mati Meron]
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

[EL]
You sound like you do know what is a group velocity so why do you also
sound as if you are endorsing the superluminal lie?

Frankly, I've no idea what you're talking about and, since you're a
nice guy, I won't even check. If you've any issues with group
velocity, feel free to consult Jackson's "Electrodynamics", chapt. 7.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"