A Possible Explanation for the Acceleration of the Universe’s Expansion without Dark Energy

Abstract

The acceleration of the expansion of the universe has been observed. To explain this phenomenon, physicists usually introduce the dark energy (DE) whose pressure is negative, or they need to modify the gravity to produce a term equivalent to the dark energy. Are there other possibilities? Combining our previous works about statistical mechanics of self-gravitating system with the derivation of van der waals equation, we propose a different matter’s equation of state (EoS) in this paper. Then, we find that if the matter’s density is low enough, its pressure can always be negative, which means that it is the matter that drives the expansion’s acceleration. So here we will not need to add the DE to the universe. Our results also predict that the universe finally will tend to be dominated by an approximately constant energy density whose value can be smaller than DE. The data of Supernova cannot differentiate our model from the standard model, but they may possibly indicate some deviations from ΛCDM.