IRREVERSIBILITY AND SPACE-TIME STRUCTURE.

Abstract

The present reconceptualization of physics implies a revision of current ideas about space and time. Classical dynamics implied a reversible, eternal time. Nineteenth-century thermodynamics implied an irreversible time associated to the degradation of energy. Irreversible processes, described by non-conservative dynamical systems, introduce spatial and temporal inhomogeneities in physical systems submitted to strong external constraints. Non-linear thermodynamics is then able to speak about the apparition of new structures, in contrast to mere conservation and/or destruction. Qualitative dynamics allows us to re-evaluation the relations between instability and irreversibility; tools like elliptic and hyperbolic points or Lyapunov exponents are used in order to build new concepts such as an 'internal time operator', or to give a thickness to present time, described as a transition layer between past and time, taking into account the essential importance of unstable systems in any physical description of nature.