Action for classical, quantum, closed and open systems

Janos Polonyi

Published 2023-07-23Version 1

The action functional can be used to define classical, quantum, closed, and open dynamics in a generalization of the variational principle and in the path integral formalism in classical and quantum dynamics, respectively. These schemes are based on an unusual feature, a formal redoubling of the degrees of freedom. Five arguments to motivate such a redoubling are put forward to demonstrate that such a formalism is natural. The common elements of the different arguments is the causal time arrow. Some lessons concerning decoherence, dissipation and the classical limits are mentioned, too.