| Summary: | 碩士 === 國立臺灣大學 === 物理學研究所 === 91 === The observations by Supernova Cosmology Project and Supernova Search Team have suggested that the expansion of the Universe is still accelerating. Although the acceleration may be driven by the existence of a positive cosmological constant (vacuum energy), there remain other interpretations of the accelerating expansion, such as quintessence and extra dimensions. In this thesis, we explore the feasibility of making use of extra dimensions in describing the evolution of universe in various eras, especially, generating the accelerating expansion of the present matter-dominated universe. We suggest that the curvature of extra dimensions is positive and that of ordinary
3-space is negative for describing the present accelerating universe. The flat higher-dimensional spacetime with the existence of a cosmological constant is not appropriate to describe the present universe on the contrary.
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