  We build quantum field theory on the thermodynamic master equation for
dissipative quantum systems. The vacuum is represented by a thermodynamic
equilibrium state in the low-temperature limit. All regularization is
consistently provided by a friction mechanism; with decreasing friction
parameter, only degrees of freedom on shorter and shorter length scales are
damped out of a quantum field theory. No divergent integrals need to be
manipulated. Renormalization occurs as a tool to refine perturbation
expansions, not to remove divergences. Relativistic covariance is recovered in
the final results. We illustrate the proposed thermodynamic approach to quantum
fields for the phi^4 theory by calculating the propagator and the beta
function, and we offer some suggestions on its application to gauge theories.
