Abstract:
According to the general theory of relativity, gravitational lensing occurs when light from the distant objects is distorted and magnified in a strong gravitational field. Many examples of gravitational lensing, including Einstein rings, have been discovered since 1980. Thanks to gravitational lensing, today's astronomers can catch sight of celestial bodies that are too far away to be observed. 700 000 years past after the Big Bang, the universe lasted next 400—500 million years when it was in dark, with the matters homogeneous in general. There were not any objects that shone. When did stars begin to emit light? From gravitational lensing, astronomers have got some information about it. Dark matter, one of two dark clouds called in 21st century, is over 4 times in mass more than whole matter we have ever known, and radiate nothing, so it is impossible to be detected directly. By means of gravitational lensing, however, we can obtain the evidence to prove the presence of such dark matter and analyze the space distribution.