Classifying the Unclassifiables

Abstract

In 1955 George Mackey suggested that there is a fundamental dichotomy in the unitary representation theory of locally compact second countable groups. He felt that there cannnot be a reasonable classification theory for the unitary representations of a group G for which the dual is a non-smooth Borel space. Mackey's precise conjecture regarding when this is the case was subsequently verified by Glimm. This approach to "classifiability" can be applied in many other branches of mathematics. Included in this article is a sketch of some of the exciting new developments that have been made in this direction. Evidence is given that there should be extensions of Mackey's ideas to such "finitistic" problems as the classification of the finite p-groups. In a different direction, Mackey's thoughts about quantization are also briefly discussed.