On the classical hydrodynamic limit of quantum field theories

TL;DR

This paper explores how classical fluid dynamics can emerge from quantum field theories without explicit system-environment separation, using coarse graining and projection methods to identify conditions for classical behavior.

Contribution

It introduces a framework for deriving classical fluid equations directly from quantum field theories through coarse graining and projection techniques.

Findings

Conditions for classical dynamics are established.

Derivation of equations of motion for a perfect classical fluid.

Application of the projection method to quantum fields.

Abstract

We discuss the transition from a quantum to a classical domain for a model where a separation into environment and system is explicitely not given. Utilizing the coarse graining procedure for free quantum fields we also apply the projection method and the Hamiltonian principle to study possible cases of emergent classicality. General conditions for classical dynamics are given. Eventually, they lead to the equations of motion for a perfect classical fluid.