Atoms and hadrons (classification problems)
A group approach is discussed for classifying two types of objects: hadrons and chemical elements. In this approach, both the hadrons and the atoms are treated as structureless particles. The groups underlying the classifications are different in the two cases: the unitary SU(3) in the hadron case and the orthogonal O(4) group in the atomic case. The classification principles, on the other hand, are identical, and in this sense there is an analogy between atoms and hadrons. Certain aspects of this analogy are discussed.