Ernest Rutherford (New ZealandBritish physicist, 18711937), the 1908 Nobel Laureate who discovered the existence of atomic nuclei, is famously quoted as having said: Physics is the only real science. All the rest is butter?y collecting. Or something to that e?ect. I like to include this quote in my introductory remarks at the ?rst class meetings of the physics courses I teach. I have seen that there are those whointerpret this as a put-down of amateurs (butter?y collectors) in science. However, my own interp- tation of Rutherfords statement is that he is claiming that, except for physics, all of the rest of science is involved merely in collecting facts and classifying them (butter?y collecting). It is physics, uniqueamong the sciences, that is attempting to ?nd explanations for the classi?ed data. The periodic table of the chemical elements, originally proposed by DmitriIvanovichMendeleev(Russianchemist,18341907), presentsan example of this. Chemists toiled to discover the chemical elements and their properties and then classi?ed the elements in the scheme that is expressed by the periodic table. Here was the chemists butter?y collecting. It took physicists to explaintheperiodictablebymeansof quantum theory.

A theoretical physicist, Joe Rosen was for many years a member of the School of Physics and Astronomy of Tel Aviv University and also served as chair of the Department of Physics and Astronomy of the University of Central Arkansas. He has authored or edited eleven books, and many of his publications have dealt with various aspects of symmetry in physics and in science. Now semi-retired from academe, Joe Rosen is involved in research, writing, and physics teaching as adjunct professor at universities and colleges in the Washington DC area.

The Concept of Symmetry.- Science Is Founded on Symmetry.- Symmetry in Physics.- The Symmetry Principle.- Application of Symmetry.- Approximate Symmetry, Spontaneous Symmetry Breaking.- Cosmic Considerations.- The Mathematics of Symmetry: Group Theory.- Group Theory Continued.- The Formalism of Symmetry.- Symmetry in Processes.- Summary of Principles.