Teaching E = mc~2: Mass Without Mass

摘要

The mass-energy relation is, according to Einstein, the most important result of the special theory of relativity. Many educators have called for the inclusion of more such "modern" (post-1900) physics in our introductory courses. Although we frequently treat E = mc~2 as a simple numerical relation, useful for solving nuclear physics problems, it is more important to discuss what this equation means. What can it tell us about the nature of energy and matter? Does rest mass arise purely from the energy of force fields? It seems not to be widely recognized that the answer to this last question is now known, at least for 90% of the mass of ordinary matter, to be "yes."