Initial Value Problem in General Relativity

Abstract: This article, written to appear as a chapter in "The Springer Handbook of Spacetime", is a review of the initial value problem for Einstein's gravitational field theory in general relativity. Designed to be accessible to graduate students who have taken a first course in general relativity, the article first discusses how to reformulate the spacetime fields and spacetime covariant field equations of Einstein's theory in terms of fields and field equations compatible with a 3+1 foliation of spacetime with spacelike hypersurfaces. It proceeds to discuss the arguments which show that the initial value problem for Einstein's theory is well-posed, in the sense that for any given set of initial data satisfying the Einstein constraint equations, there is a (maximal) spacetime solution of the full set of Einstein equations, compatible with the given set of data. The article then describes how to generate initial data sets which satisfy the Einstein constraints, using the conformal (and conformal thin sandwich) method, and using gluing techniques. The article concludes with comments regarding stability and long term behavior of solutions of Einstein's equations generated via the initial value problem.