Energy travels at group velocity and not phase velocity?

AI Thread Summary
Energy travels at group velocity rather than phase velocity, as group velocity represents the speed at which the envelope of a wave packet moves, correlating with energy transfer. However, it is important to note that group velocity does not always equate to the speed of energy transfer in all scenarios. A general proof supporting this concept can be found in a referenced paper discussing the equivalence of group velocity and energy transport. The discussion emphasizes the need to understand the conditions under which group velocity accurately reflects energy movement. Overall, the relationship between group velocity and energy transfer is complex and context-dependent.
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How to prove that energy travels at group velocity and not phase velocity?
 
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Start here: http://en.wikipedia.org/wiki/Group_velocity

Note that the group velocity is not always the speed for energy transfer!

A general proof is given in this paper: http://journals.aps.org/archive/abstract/10.1103/PhysRev.105.1129
"General Theorems on the Equivalence of Group Velocity and Energy Transport"
 
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