Geons: http://en.wikipedia.org/wiki/Geon_(physics [Broken]) From the above: "In theoretical general relativity, a geon is an electromagnetic or gravitational wave which is held together in a confined region by the gravitational attraction of its own field energy. They were first investigated theoretically in 1955 by J. A. Wheeler, who coined the term as a contraction of "gravitational electromagnetic entity." Since general relativity is a classical field theory, Wheeler's concept of a geon does not treat them as quantum-mechanical entities, and this generally remains true today. Nonetheless, Wheeler speculated that there might be a relationship between microscopic geons and elementary particles. This idea continues to attract some attention among physicists, but in the absence of a viable theory of quantum gravity, the accuracy of this speculative idea cannot be tested. However recently Sundance Bilson-Thompson, Fotini Markopoulou and Lee Smolin, in the context of Loop Quantum Gravity discovered some objects very similar to the Wheeler idea of geon. ..." Are there solutions of general relativity that act like particles, remain unchanged for large time and are localized? Do these solutions come in all "sizes"? Do geons interact gravitationally with other geons? What rules out these guys from being our missing mass? Thanks for your thoughts.