Editing Fluctuation theorem (section)

== Nonequilibrium partition identity ==

Another remarkably simple and elegant consequence of the fluctuation theorem is the so-called "[[nonequilibrium partition identity]]" (NPI):<ref>{{cite journal|last=Carberry|first=D. M.|author2=Williams, S. R. |author3=Wang, G. M. |author4=Sevick, E. M. |author5=Evans, Denis J. |title=The Kawasaki identity and the Fluctuation Theorem|journal=The Journal of Chemical Physics|date=1 January 2004|volume=121|issue=17|pages=8179–82|doi=10.1063/1.1802211|pmid=15511135|bibcode = 2004JChPh.121.8179C |url=http://espace.library.uq.edu.au/view/UQ:298976/UQ298976_OA.pdf|hdl=1885/15803|hdl-access=free}}</ref>
: <math> \left\langle {\exp [ - \overline \Sigma_t \; t ]} \right\rangle  = 1,\quad \text{ for all } t .</math>

Thus in spite of the second law inequality, which might lead you to expect that the average would decay exponentially with time, the exponential probability ratio  given by the FT ''exactly'' cancels the negative exponential in the average above leading to an average which is unity for all time.