Discussed is the present concept of the ultimate nature of matter--the elementary particle. An explanation is given for why the lepton family of particles--the electron, muon, and tau--may be truly elementary. The tau lepton is described in more detail. (Author/DS)

Traces the history of the search for the ultimate nature of matter. The work of outstanding physicists since the late nineteenth century is discussed as it relates to the total picture of the search for a single unifying theory. (SA)

Science has many explanatory concepts that have been proposed to account for the observable features of things. Such explanatory concepts often have associated with them hidden or unseen "theoretical entities." The electron is a key concept in understanding phenomena described by science. The question arises, however, as to how students…

Answers a student's question about the emission of a positron from a nucleus. Discusses the problem from the aspects of the uncertainty principle, beta decay, the Fermi Theory, and modern physics. (YP)