On the statistical description of quantum systems

Luciano Colombo

Yuri A. Rylov

Hamilton variational principle for special type of statistical ensemble of deterministic dynamical systems is derived. Thie form of variational principle allows one to describe the statistical ensemble in terms of wave functions and provides a basis for a description of statistical ensemble of stochastic systems. It is shown that sometimes such a statistical description of stochastic particle motion appears to coincide with the quantum description in terms of Schroedinger equation.

T. Bergstein

From the preceding exposition it follows that the quantum statistical representation of an individual atomic system does not imply any renunciation regarding further knowledge about the system. On the contrary the statistical character of quantum physics directly reflects the fundamental non-causal appearance of quantal recordings, and through the discovery of the complementarity of quantal phenomena a complete but necessarily statistical description of the atom has been accomplished. Furthermore quantum physics has afforded a statistical description of macroscopic bodies through their representation as assemblies of huge numbers of identical atomic systems, and, apart from accounting in a more fundamental way for the properties already described in classical physics(the correspondence principle, p. 36), quantum statistics explains several macroscopic phenomena which cannot be understood within the conceptual frame of classical physics only. It must be maintained, however, that when observing the properties of individual atomic objects the macroscopic observational apparatus cannot be represented in terms of atomic constituents because this would destroy the unambiguity of the description. The observational apparatus fulfils its basic function of being the spacetime frame of reference for the quantal recordings precisely through its description in classical physics alone. However, when refraining from the analysis of individual quantal processes it is possible to apply quantum statistics to macroscopic phenomena, that is, the causality of classical physical phenomena can be interpreted in the quantum formalism as the statistical result of the interplay of enormous numbers of atomic processes. It is possible, then, to talk of statistical causality as a fundamental aspect of physical reality.

B. Freedman. Physics Department

M Reginatto, M J W Hall

We provide an overview of a canonical formalism that describes mixed quantum-classical systems in terms of statistical ensembles on configuration space, and discuss applications to measurement theory. It is shown that the formalism allows a general description of the measurement of a quantum system by a classical apparatus without running into inconsistencies. An example of classical and quantum particles interacting gravitationally is also given.