Effective field theories of non-equilibrium physics

Non equilibrium effective field theory is presented as an inhomogeneous field theory, using a formulation which is analogous to that of a gauge theory. This formulation underlines the importance of structural aspects of non-equilibrium, effective field theories. It is shown that, unless proper attention is paid to such structural features, hugely different answers can be obtained for a given model. The exactly soluble two-level atom is used as an example of both the covariant methodology and of the conclusions.