Gravity Theory From The Thermodynamical Viewpoint

According to the quantum field theory in curved space-time, one can investigate that black holes and other space-time models all have thermodynamic effects. Based on the thermal properties of space-time, we confirm that space-time, as well as the other matters, has inner microscopic structure. So some physicists think that the theory of gravity describing the space-time may be only an emergent phenomenon, such as Verlinde's entropic force scenario which explains that the origin of the gravity is entropic differences on the holographic screen. In this thesis, in order to obtain some new predictable gravitational phenomena, we argue several ones which can't be induced from traditional pure theory of gravity, e.g. gravitational fluctuations.In chapter1, we briefly introduce the background and sense of investigations, and review the history of understanding the nature of gravity and connection between space-time and thermodynamics. Besides, we propose some our own opinions, leading to the conclusion that the gravity is an emergent phenomenon.In chapter2, a few views of emergent gravity are analyzed in detail. We also give some specific mathematical derivations. Among that, we introduce how to understand space-time and gravity in the view of the thermodynamics and focus on the analysis of the inspiration from the holographic principle. In addition, Verlinde's entropic force scenario is also analyzed emphatically. After that, we point out some defects of entropic force and its solutions.In the next chapter, we modify Newtonian gravitational theorem by the use of the modified equipartition energy theorem. In this chapter, space-time is in analogy with elastic solid mainly based on solid in order to modify entropic force. Then we derive the modified Newtonian theorem and discuss that the implications and physical senses of the correction term are reflecting the fluctuations of the space-time.In the fourth chapter, we apply the modified entropic force and gravitational fluctuation phenomena to cosmology and get the modified Friedmann equation. The correction term, as well as cosmological constant, can be explained as vacuum energy density. Furthermore we can get the exact form of vacuum energy density ρ0～hωD*which coincides with the result from quantum field theory. So, we believe that the cosmological constant probably reflects the fluctuations of the space-time.At last, we summarize this thesis and make some prospect...