Sample exams, with solutions, are available to help MIT Physics doctoral students study for the Written Exam. General relativity takes the form of field equations, describing the curvature of space-time and the distribution of matter throughout space-time. Gravitons are theorised by looking at the linearisation of a perturbation of curved spacetime and it turns out that it is a massless spin-2 particle. In general relativity, an exact solution is a solution of the Einstein field equations whose derivation does not invoke simplifying assumptions, though the starting point for that derivation may be an idealized case like a perfectly spherical shape of matter. Solutions can also be organized using the Segre classification of the possible algebraic symmetries of the Ricci tensor: The remaining Segre types have no particular physical interpretation and most of them cannot correspond to any known type of contribution to the stressenergy tensor. Online reference material can be found at. Classical Theory of Fields, by Landau and Lifschitz. They are a lightly edited version of notes I handed out while teaching Physics 8.962, the graduate course in GR at MIT, during the Spring of 1996.