Quantum Chaos and the Foundations of Statistical Mechanics

Understanding the emergence of the rules of statistical mechanics for an isolated many-body system from an underlying quantum-mechanical microdynamics is a longstanding problem of fundamental physics. 

Concepts from the theory of quantized classically chaotic systems can be used to resolve at least some of the key issues, and lead to the notion of “eigenstate thermalization” : individual energy eigenstates of the system as a whole appear to be states of thermal equilibrium when probed by local (few-body) observables.