group velocity
Noun
Meaning
group velocity (plural group velocities)
(physics) the propagation velocity of the envelope of a modulated travelling wave, which is considered as the propagation velocity of information or energy contained in it.
Examples
Because the group velocity varies with k, the shape of the wave packet broadens with time, and the particle becomes less localized.
Because the group velocity for such a field is superluminal, naively it appears that its excitations propagate faster than light.
By contrast, tachyonic fields - quantum fields with imaginary mass - certainly do exist, and exhibit superluminal group velocity under some circumstances.
Consequently, for that wave situation, the group velocity is : showing that the velocity of a localized particle in quantum mechanics is its group velocity.
However, it is not the group velocity but the signal velocity that determines the communication speed, and superluminal group velocity does not imply superluminal signal velocity.
However, it was quickly understood that the superluminal group velocity does not correspond to the speed of propagation of any localized excitation (like a particle).