The key element of modern cosmology is the assumption that the General Theory of Relativity (GR) is the correct theory of gravitation. It replaced the Newtonian theory of gravity which was presented in the Principia in 1687. The fundamental idea in GR is that gravity is a manifestation of the curvature of the spacetime, while in Newton’s theory gravity acts directly as a force between bodies. Many of the predictions of GR, such as the bending of star light by gravity and a tiny shift in the orbit of the planetMercury, have been quantitatively confirmed by experiment
Reference:
Abdelwahab, M. 2012. Topics in modified gravity. University of Cape Town.
Abdelwahab, M. E. S. (2012). Topics in modified gravity. (Thesis). University of Cape Town ,Faculty of Science ,Department of Mathematics and Applied Mathematics. Retrieved from http://hdl.handle.net/11427/4956
Abdelwahab, Mohamed Elshazli Sirelakhatim. "Topics in modified gravity." Thesis., University of Cape Town ,Faculty of Science ,Department of Mathematics and Applied Mathematics, 2012. http://hdl.handle.net/11427/4956
Abdelwahab MES. Topics in modified gravity. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Mathematics and Applied Mathematics, 2012 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/4956