宇宙学文献综述

Dark energy

A lot of astronomical observations indicate that the universe is flat,and consists of 4% baryon matter,23% dark matter,72% dark energy and negligible radiation matters. 1 what is dark energy on earth ?To describe the dark energy,the equation of state whas to satisfy w ,it is interesting to note that it is not an easy job to find a suitable candidate for the dark energy.The simple one is a small cosmological constant ,but it is difficult to understand why smaller than the expected value about 120 order. This is the so-called cosmological constant problem.Another problem about the dark energy is called the coincidence problems that why dark energy density and dark matter density are in the same order?Because the two evolution with the cosmic time are so different. In recent years the dark energy problem has become the most active and important one in the field of research in the modern cosmology.

Dark energy discovery

The most direct evidence of cosmic acceleration is fromⅠa type supernova observation, this type of supernova can be used as a standard candlelight.People found in distant red shift ( between 0 to 2), Ⅰa type of supernova’s luminance darker than originally expected ,this means these supernovae are further from us than before. Not as the big bang model predicted ,our the universe expansion is not slowing down but speeding up. To explain the cosmic acceleration people usually introduce dark energy which has negative pressure . But people first have reason to thoroughly inspect . Whether Ⅰa type of supernova's brightness dimmer than before really means universe's expansion is accelerating.If there are other mechanism to explain,the dark energy is not necessary. During these years people put forward some theory that don't need to introduce dark energy to explain the supernova’s luminosity darker mechanism" such as gray dust, photon axion conversion, and the luminosity evolution, but in recent years more and more high precision supernova and other astronomical observations such as microwave background fluctuations, large scale structure have been greatly compressed these explain’s living space.