The General Theory of Relativity and Its Tests in the Solar System

The general theory of relativity (GR) has had a number of experimental and theoretical triumphs, from very accurate tests in the solar system and astrophysical tests to the prediction and observation of the expansion of the universe, of gravitational waves and black holes. Furthermore, GR has today practical applications in space research, geodesy, astronomy and navigation in the solar system. Despite its experimental and theoretical triumphs, GR has some open underlying problems. GR is incompatible with quantum mechanics. Furthermore, it predicts the occurrence of spacetime singularities where every known physical theory ceases to be valid and time ends. In cosmology, observations of distant supernovae have led to the discovery of the mysterious accelerated expansion of the universe. Possible explanations of such a riddle involve a cosmological constant, “dark energy”, “quintessence” or modifications of GR. For these reasons, there are today a number of experiments to improve the accuracy of the tests of GR and of alternative gravitational theories. In this chapter we describe the main past, present and future tests of GR in the solar system.