Notes
The author wishes to thank Mark Mullen and James Toevs of the Los Alamos National Laboratory for helpful discussions leading to the development of many of the ideas presented here. He also thanks Matt Bunn, Leonard Spector, and William C. Potter for their critical reading of the manuscript and their helpful comments and suggestions. The opinions expressed in this article are those of the author and do not necessarily represent those of the laboratory, the U.S. Department of Energy, or the U.S. government.