Confusing biological rhythms and physical clocks Today's ecological relevance of Bergson-Einstein debate on time

International audienceThe reflections on the nature of time in Relativity Theory will be hinted in reference to the new bridges recently proposed by Connes and by Rovelli's 'perspectival' approach, two major steps towards a unification of quantum, thermodynamical and relativistic times. The so called "time of philosophers", a time of the cognizing ego, from Saint Augustin to Husserl and Bergson, is based on a different, but relevant perspective and it has been traditionally opposed to the 'time of physicists'. In between these two approaches, we discuss a proper time of phylogeny and ontogeny, in biology, with their own rhythms and specific irreversibility. On the one side, biological time needs to be scientifically objectivised as an invariant of the knowing subject and thus move, as in physics, 'from the subjectiveabsolute to the objective-relative' (Weyl's approach, extended to time). On the other, we propose a 'geometry' of life's rhythms and an 'extended present' that radically differ from the prevailing spatialization of physical time that Bergson soundly criticizes. The proper irreversibility and the central, 'operatorial', role of time in biology will be stressed, as nothing in biology can be understood except in the light of a temporal perspective, both evolutionary and organismal. In particular, today's ecosystemic changes bring to the limelight some disruptions of the evolutionary fine-tuning of biological rhythms and physical clocks that may be better understood by highlighting their theoretical differences as well as their environmental interactions. It is to the credit of Bergson's philosophy to have pointed out forcefully this deep division between the world of mathematical concepts and the immediately experienced continuity of phenomenal time ('la durée'