Research On Some Problems In Modern Cosmology

The main aims of modern cosmology are researching the structure of large scale spacetime and the evolution of our universe. In this paper, we firstly review the history from beginning of 20 century up to now, and enumerate several important observed results of astronomy, such as redshift of galaxy, Cosmic Microwave Background (CMB) radiation etc, and these results prove the theoretical elements of modern cosmology. Furthermore, we review the standard model of modern cosmology―Friedmann model. The model based on general relativity obeys the cosmological principle and describes the evolution of the universe. At the same time, we introduce the inflationary model of the early universe that be accepted widely. We present the new explanation of the cosmological constant problem. Considering a spacetime with extra spatial dimensions, we interpret the deduced interaction term of the general dimensions and extra spatial dimensions as the cosmological constant. In this way, we not only present a reasonable origin of the cosmological constant, but get a cosmological constant consistent with the observed data by calculating a simple model that has 3 extra dimensions. On the other hand, the explanation accords with the recent idea that there may exist large extra dimensions in superstring theory. We deduce a new Friedmann equation that relative with extra dimensions from a n-dimensional spacetime. By comparing the new Friedmann equation with the old one, we get a relation equation of scale factors of the general dimensions and extra dimensions. Considering the condition without matter, we get solutions of scale factor of 3 spatial dimensions and that of extra spatial dimensions. Finally, we discuss the cosmological parameters expressed by scale factor of extra dimensions and get the results consistent with the observational data.