How do particle systems heat up? A physics framework for universal thermal behavior

When any collection of particles thermalizes, complex microscopic dynamics collapse into universal hydrodynamic laws—analogous to how air pressure emerges from trillions of molecular collisions. These lectures develop effective field theory (EFT) tools to calculate this emergence quantitatively, treating hydrodynamic equations themselves as weakly-coupled effective theories. The framework unifies examples from quantum spin chains to relativistic plasmas, and reveals constraints on transport coefficients (like viscosity) from fundamental symmetries and quantum anomalies.