Vol. 7, Issue 1, Part C (2025)

The early universe went through the rapid and transforming processes especially the inflation and the reheating processes which are nonequilibrium processes that involve irreversible energy dissipation and entropy increase. Cosmic phase transitions have only been comprehended using a paradigm that goes beyond conventional equilibrium thermodynamics. The research paper explores the concept of entropy production as a quantitative method of measuring irreversibility during the inflation and reheating periods, which gives some understanding of the dynamics of the early universe. Analytical mean-field methods combined with numerical simulations were used to calculate entropy production of continuous (second-order) and discontinuous (first-order) transitions with different potential shapes, initial conditions and strengths of interaction using a scalar field model of the inflation. Findings reveal that the rate of production of entropy rises slowly during inflation, which is characterized by moderately irreversible energy dissipation, whereas the process of reheating is characterized by a steep rise because of the quick transfer of energy through the inflation to radiation. Initial field values and potential parameters are very strong factors that affect peak entropy. These results prove the use of entropy production to be a potent vessel in the classification of cosmic phase transitions, the connection between nonequilibrium thermodynamics and the cosmological evolution and observable effects including the cosmic microwave background