# Nonextensive statistical mechanics

I know that the Tsallis($S_q$) entropy is called nonextensive information measure in the sense that if $P$ and $Q$ are two probability distributions then $S_q(P\times Q)=S_q(P)+S_q(Q)+(1-q)S_q(P)S_q(Q)$. My question is what is meant by nonextensive statistical physics? What is its connection with Tsallis entropy maximisation?

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Hi Ashok, welcome to Physics Stack Exchange! On this site each individual question should be posted separately, so I removed your second item from this post. I encourage you to post it as a separate question. –  David Z Sep 19 '11 at 5:28
Thanks David Zaslavsky. –  Ashok Sep 19 '11 at 6:42

Also, what I find misleading about the non-additive formula for $S(P\times Q)$ is that it tries to pretend that $S(P\times Q\times R)$ have to be determined after that. Effectively, the formula introduces some "two-body-interaction-like" modifications of entropy but pretends that there isn't any three-body or higher-body interaction. This is just meaningless. And the more complex interactions - which are really relevant for the very-many-body entropy - do matter. At most, this business may inspire one to get some new probability distributions but there are infinity of others, too. –  Luboš Motl Feb 1 '12 at 6:40