Brading, Katherine. Symmetry and Symmetry Breaking
Introduction: Symmetry considerations dominate modern fundamental physics, both in quantum theory and in relativity. Philosophers are now beginning to devote increasing attention to such issues as the significance of gauge symmetry, quantum particle identity in the light of permutation symmetry, how to make sense of parity violation, the role of symmetry breaking, the empirical status of symmetry principles, and so forth. These issues relate directly to traditional problems in the philosophy of science, including the status of the laws of nature, the relationships between mathematics, physical theory, and the world, and the extent to which mathematics suggests new physics.
This entry begins with a brief description of the historical roots and emergence of the concept of symmetry that is at work in modern science. It then turns to the application of this concept to physics, distinguishing between two different uses of symmetry: symmetry principles versus symmetry arguments. It mentions the different varieties of physical symmetries, outlining the ways in which they were introduced into physics. Then, stepping back from the details of the various symmetries, it makes some remarks of a general nature concerning the status and significance of symmetries in physics.
Comment: This article offers a good introduction to the topic of symmetries. The entry begins with a brief description of the historical roots and emergence of the concept of symmetry that could serve as a reading for undergraduates. It then turns to the application of this concept to physics and merges the discussion with issues in relativity and quantum mechanics. This second part of the article is thus more suitable to postgraduate courses in philosophy of science, specially, philosophy of physics. It could serve as a secondary reading for those researching the laws of nature.