Velocity correlations and irreversibility: a molecular dynamics approach

It is a great privilege to contribute to this volume dedicated to Benno Hess. The impact of his work goes far beyond biochemistry. It has stressed the importance of the role of time and irreversibility in the description of biological and chemical systems. This is now well accepted on the phenomenological level. However the relation of irreversibility with the underlying microscopic dynamics remains a subject of some controversy. Let us remember the classical point of view expressed concisely by Smoluchowski /1/: “If we continued our observation for an immeasurably long time, all processes would appear to be reversible”. With Smoluchowski, Chandrasekhar /2/ concludes that “a process appears irreversible (or reversible) according to whether the initial state is characterized by a long (short) average time of recurrence compared to the time during which the system is under observation”. Irreversibility would then appear as an artifact due to the time scale of observation!Also at the Centre for Statistical Mechanics and Thermodynamics, the University of Texas at Austin.NOTXT