Complex sentence: Many natural systems still today remain beyond the scope of currently known macroscopic thermodynamic methods; the fundamental difficulty for macroscopic thermodynamics is in defining entropy for systems not in thermodynamic equilibrium Grandy, W.T., Jr (2008).
Split into simpler sentences: Many natural systems still today remain beyond the scope of currently known macroscopic thermodynamic methods. Amongst others, one fundamental difficulty is in defining entropy in macroscopic terms for systems not in thermodynamic equilibrium Grandy, W.T., Jr (2008).