Tra essere e divenire. Oltre il paradosso dell’irreversibilità

The relation between the dynamical reversibility and the thermodynamic irreversibility is analysed from a historical, theoretical and epistemological point of view. The current approaches to the problem are confronted and criticized. The first aims at a reduction of the thermal phenomena to the mechanical reversible properties of elementary constituents of bodies. The other introduces at the microscopic level some irreversible intrinsic hypothesis by which to deduce the macroscopic irreversibility. However, these approaches fail to deduce the thermodynamic irreversibility independently on the recourse to a subjective interpretation of the probabilities involved in the thermal (objective) phenomena. Moreover, recent works show that the thermodynamic irreversible phenomena are independent on the microscopic properties of bodies. The reduction of the macroscopic level to the microscopic one seems to be impossible. The statistical description must have the same objectivity of the dynamical one and the complementarity idea is the best tool for the construction of a scheme that allows the existence of a plurality of descriptions. The complementarity between dynamical and statistical description of macroscopic bodies, that depends on the number of microscopic constituents must not be confused with the similar relations proper of quantum mechanics (see Heisenberg's uncertainty relations) and statistical thermodynamics (Landau's uncertainty relations for the fluctuations of macroscopic quantities). These two last relations operate at the microscopic and at the macroscopic levels, respectively, whereas the dynamical-statistical complementarity is a meta-relation between the two levels of description. From these considerations some epistemological consequence are drawn: 1] Physical phenomena request a plurality of levels of description in order to take into account the emergence and the disappearance of physical properties into the transition from one level to another. 2] Both reductionist and systemic modes of thought are necessary for our description of experience. 3] Our criteria of rationality must be generalized in order to take into account the evolutionary development of our concepts and conceptual structures.