Investigation On The Deviation Of Vacuum Refractive Index And The Propagation Characteristic Of Light In Gravitational Field

Since the establishment of general relativity, quite a number of observations have supported this theory of gravitation. Nevertheless, physicists believe that nature is unified, and therefore the four fundamental interactions, i.e., the gravitational force, the electromagnetic force, the weak force and the strong force, should be described by a unified theory. Einstein himself devoted the second half of his life in quest of a unified field theory for the gravitation and the electromagnetism, but he failed at last. Now, the electromagnetic, the weak and the strong forces have already been unified in a quantum framework, whereas the quantization of gravitational field is still faced with the vital problem of infinities after more than 70 years of hard attempts.On the other hand, the modern astrophysics and cosmology are confronted with two challenging problems—the dark matter and dark energy, related to a series of puzzles such as the abnormal rotation curve of a galaxy, the accelerated expansion of the universe and so on. These problems together with the infinities in the quantization of gravitational field indicate strongly that there must be a rigorous examination of Einstein's geometrized theory of gravitation, especially a careful investigation of the role of vacuum in gravitational interaction.In view of the above reasons and in order to demonstrate that a vacuum based theory of gravitation is workable, this dissertation will present a basic remark on the physical characteristics of the quantum vacuum, investigate the propagation characteristic of light in gravitational field by using a graded refractive index of vacuum, and apply the obtained results to analyze gravitational lensing in a conventional optical way. The original work done in this thesis is as follows:(1) A new proposal that vacuum may be the medium of gravitational interaction, and that vacuum may be influenced by gravitational matter is put forward. In this proposal, we believe an inhomogeneous vacuum in gravitational field. An inhomogeneous vacuum may be the physical reality of the curved spacetime, this idea comes from the similarity between the Fermat principle for light propagation in a gravitational field and that in an inhomogeneous medium.(2) A general method for calculating the vacuum refractive index in gravitational field is found, by comparison of the angular displacement formula for light propagation in a curved spacetime with that in an inhomogeneous vacuum. The vacuum refractive index profile for outside and inside the gravitational matter system is derived from the Schwarzschild exterior and interior solutions. A simple unified exponential function of gravitational potential is obtained for these two refractive index profiles in weak field cases, and thus the curved spacetime, the inhomogeneous vacuum and the gravitational potential are related together.(3) Gravitational lensing is investigated by using the obtained refractive index of vacuum. The ray path, the image shape, the time delay between the upper and lower images, the mass of the lens body and the Hubble constant are analyzed in a conventional optical way. The central imaging of gravitational lensing is studied in the same way. The long-standing puzzle of the central image being missing in almost all known cases of gravitational lensing is answered clearly.