Short-time behavior and universality in irreversible models

We discuss the issue of universality in nonequilibrium phase transitions. We present an introduction to the approach of statistical mechanics that is grounded in the construction and analysis of stochastic lattice models. The concept of irreversibility is studied through the analysis of the condition of detailed balance. The role of symmetry and irreversibility on the critical behavior of the nonequilibrium models is examined. We focus on short-time universal behavior of reversible and irreversible models.