Molecules May Explain the Expansion of the Universe

The Hubble diagram continues to remain one of the most important graphical representations in the realm of astronomy and cosmology right from its genesis that depicts the velocity-distance relation for the receding large-scale structures within the Universe; it is the diagram that helps us to understand the Universe’s expansion. In this paper I introduce the molecular expansion model in order to explain the expansion of the Universe. The molecular expansion model considers the large-scale structures as gas molecules undergoing free expansion. Since large-scale structures are ensemble of atoms, therefore, they must behave like molecules possessing finite amount of energy. Instead of considering that space is expanding, the paper emphasizes upon the actual recession of large-scale structures. I show in this paper that the linear velocity-distance relation or the Hubble diagram is actually a natural feature of gas molecules undergoing free expansion. Molecules being natural entities provide a natural and viable explanation. The study conducted in this paper finds the recessional behaviour of large-scale structures to be consistent with the recessional behaviour of molecules. The free expansion of gas molecules is found to be homogeneous, isotropic and in agreement with the Copernican principle. Redshift-distance relationship has been plotted for 580 type Ia supernovae from the Supernova Cosmology Project data and the reason for the deviation of the Hubble diagram from linearity at high redshifts has been explained by introducing the concept of differential molecular expansion