The Contour Idea for Time-Dependent Averages: Forward and Backward Branches
Abstract
This chapter introduces the contour Schwinger–Keldysh method for time-dependent averages, in light of its relevance to nonequilibrium processes. A key feature of this approach is that it leaves open the possibility that no state of a system in the future can be identified with any of its states in the past. This method is here illustrated in detail with reference to time-dependent quantum averages, whereby for definiteness the system is initially prepared at the reference time t ₀ in a definite quantum state.
Fields of Study & Subjects
Advanced Thermodynamics and Statistical Mechanics
Quantum many-body systems
Quantum Mechanics and Applications
Publication details
- Journal / source
- Cambridge University Press eBooks
- Pages
- 31–35
- Publication date
- 6 February 2026
- Document type
- Book chapter