Key points are not available for this paper at this time.
This article appears in the following collections:Letters from the Past - A PRL Retrospective2008 marked PRL’s 50th anniversary. As part of the celebrations a collection of milestone Letters was started. The collection contains Letters that have made long-lived contributions to physics, either by announcing significant discoveries, or by initiating new areas of research.2015 - General Relativity’s CentennialThe editors of the Physical Review journals have curated a collection of landmark papers on General Relativity to celebrate its centennial.
R. P. Kerr (1963) studied this question.