In search of entropy

Entropy is a quantity characterizing the arrow of time in the evolution of a physical system - in every irreversible process the entropy increases. In elementary interactions such as relativistic collision of two atomic nuclei there is considerable particle production and hence entropy production. We address here a number of questions which arise naturally in this context. When and how is entropy produced in a quantum process, such as is a nuclear collision? How is the particle production related to entropy production? How does one measure the entropy produced in the reaction? We also consider certain fundamental approaches to the problem of entropy definition in quantum physics. (author). 15 refs., 5 figs