Thermodynamic Equilibrium and Rise of Complexity in an Accelerated Universe

Observational data (Supernovae type Ia data) indicate that the rate of the universe expansion is increasing, which means that, in the framework of General Relativity, the current phase of the expansion is due to an unknown source of energy. Therefore, the nature of dominated fluid in cosmos, as the source of energy, is mysterious. Here, by considering this property of current accelerating phase along with the concept of thermodynamics equilibrium we try to find possible values for the state parameter (omega) of the dominated fluid in a (n+1)-dimensional Friedmann-Robertson-Walker universe. Our results are compatible with previous work for Gauss-Bonnet gravity and point to a universe which is so close to its thermodynamic equilibrium state. By the evolution of the cosmos, the baryonic content of the cosmos is participating in longer range interactions, including gravity and electromagnetism, and structure formation is begun which leads to an increase in the complexity content of the universe. Therefore, a true model for the cosmos should show this rise of complexity and information. In order to achieve this goal, we introduce a simple model including free particles in an expanding box and try to count the number of the states of energy. This configuration shows that the entropy of these number of states as the measure for complexity is increased when dominated fluid satisfies special condition (omega a parts per thousand yen -1) which is compatible with the results of the Supernovae type Ia data and the thermodynamic equilibrium conditions. Finally, We see that the rate of increase in the complexity content of the universe increases in the limit.