Self-Creation Gravity Versus General Relativity: a Cosmological Comparison

In the context of the self-creation theory of gravitation and its counterpart, the relativity theory, we examine their associated Bianchi-type $$VI_{0}$$ cosmological models by considering the existence of electromagnetic fields. The solution of the Einstein equations is presented by assuming that the cosmological model leads to a constant deceleration parameter ( $$q=\textrm{const}$$ ). There is no restriction on the pressure and density for the solution derived (i.e., the equation of state is not used). The technique of obtaining the scalar field $$\phi$$ is different from that used in the previous investigation. A law that shows the effect of the electromagnetic field on the entropy of the universe is derived. The entropy introduced in the two theories is a consequence of the second law of thermodynamics. Consequently, the well-known thermodynamic functions of the universe are revisited. The scalar field introduced in the self-creation theory give a good explanation for the entropy and other thermodynamics functions of the universe as compared to general relativity. Moreover, in the absence of the electromagnetic field, the solution obtained in the self-creation theory and in general relativity indicate a radiation model, provided that the obtained models, whether expressed geometrically or physically are displayed.