The macroscopic fluctuation theory deals with out-of-equilibrium systems, and it allows finding among others, the integrated current probability density. While explicitly calculating the probability density with the macroscopic fluctuation theory proves difficult, the additivity principle assumption allows to compute it more easily. Moreover, it gives rise to several universal results [1] regarding the current probability density. 

In this short talk, we will extend the Le Chatelier principle to out-of-equilibrium systems and use it to explore the validity of the additivity principle in open systems. 

[1] E. Akkermans, T. Bodineau, B. Derrida, O. Shpielberg, Universal current fluctuations in the symmetric exclusion process and other diffusive                          systems. EPL 103, 20001 (2013)