An Elementary Introduction to Relativistic Gravitation

An elementary and non-technical introduction to General Relativity and other theories of relativistic gravitation is given. Starting from simple considerations on special relativity and ordinary newtonian gravitation, it is shown how and why the need for a curved spacetime appears in the description of relativistic gravitation. With the help of examples of obviously curved spaces, such a notion is given an intuitive meaning. Next the basic principle of relativistic gravitation, i.e. the equivalence principle, is introduced and commented with some details. Using the Post-Parametrized Newtonian (PPN) formalism, light rays curvature in the vicinity of large masses, redshift of photons in a gravitational field, etc. are obtained. In the last chapter, the equations of general relativity - Einstein's equations - are given and commented.