Individual vs Group velocity

[blike]

Whats the difference between individual and group velocity?

 

This question comes in response to faf's news article "According to the latest research published in Applied Physical Letters, MTSU scientists used a setup that cost about $500 to set up a system that brteaks the speed of light (group velocity, not individual particles). "

 

So...is this a big thing or not?

[fafalone]

It's a step forward towards faster communications, but it's not an earth shattering revolution. In fact, they only propagate the group at 4x c, other projects have gotten to 400x c.

 

The signal is composed of electrons. None of the electrons ever travel faster than light here, but the message (group) reaches teh destination as if it were travelling faster than light.