Research Of Thermodynamics On Apparent Horizon In Cosmology

Since the 1980s, people have made much scientific research on cosmology. Based on astronomical observation and physical regulation, the cosmological theory has been established deeply. About the origin of cosmology, it takes the viewpoint of big bounce, as opposed to a singular big bang, which has brought us great conveniences in theoretical work. The thermodynamics of 5D big bounce universe and Horava-Lifshitz universe are key contents and also highlights of this paper.In chapter 1, it introduces the astronomical observation evidences of cosmology and cosmology model with a cosmological constant A, higher dimensional gravity theory and Horava-Lifshitz gravity theory which are related to this paper.In chapter 2, it researches apparent horizon in Friedmann-Robeitson-Walker universe, by thermodynamic method, we successfully obtain Einstein gravitational equations.In chapter 3, we construct the bridge between big bounce thermodynamics and gravitational field, finding first law of thermodynamics could be given by gravitational equations in big bounce universe. Similar with scale factor of big bounce universe, apparent horizon also contracts before bounce time and expands after it. In the meantime, we find there is only one geometry containing a 4D de Sitter universe with a general state parameter.In chapter 4, we discuss thermodynamic behavior near apparent horizon in infrared modified HL gravity. As the non-renormalization property of HL gravity, we cannot directly get the gravitational equations by thermodynamic method. According to the calculation of generalized Misner-Sharp mass, we successfully obtain Einstein gravitational equations in HL universe by first law of thermodynamics, solving the puzzle of how to construct the connections between thermodynamics and gravitational field in HL gravityAbove results aim to solve the problem of gravity and thermodynamics. For different object, using different method, and getting the related results. This is the procedure of physical work. All of the results in this paper provide rich references for further work in the future, and also provide some theory materials to research the origin of universe.