Abstract:
This talk will highlight links between topics studied in undergraduate mathematics on one hand and frontiers of current research in analysis and symmetry on the other. The approach will be semi-historical and will aim to give an impression of what the research is about.
Fundamental ideas in calculus, such as continuity, differentiation and integration, are first encountered in the setting of functions on the real line. In addition to topological properties of the line, the algebraic properties of being a group and a field, that the set of real numbers possesses, are also important. These properties express symmetries of the set of real numbers, and it turns out that this combination of calculus, algebra and symmetry extends to the setting of functions on locally compact groups, of which the group of rotations of a sphere and the group of automorphisms of a locally finite graph are examples. Not only do these groups frequently occur in applications, but theorems established prior to 1955 show that they are exactly the groups that support integration and differentiation.
Integration and continuity of functions on the circle and the group of rotations of the circle are the basic ingredients for Fourier analysis, which deals with convolution function algebras supported on the circle. Since these basic ingredients extend to locally compact groups, so do the methods of Fourier analysis, and the study of convolution algebras on these groups is known as harmonic analysis. Indeed, there is such a close connection between harmonic analysis and locally compact groups that any locally compact group may be recovered from the convolution algebras that it carries. This fact has recently been exploited with the creation of a theory of `locally compact quantum groups' that axiomatises properties of the algebras appearing in harmonic analysis and does away with the underlying group.
Locally compact groups have a rich structure theory in which significant advances are also currently being made. This theory divides into two cases: when the group is a connected topological space and when it is totally disconnected. The connected case has been well understood since the solution of Hilbert's Fifth Problem in the 1950's, which showed that they are essentially Lie groups. (Lie groups form the symmetries of smooth structures occurring in physics and underpinned, for example, the prediction of the existence of the Higgs boson.) For a long time it was thought that little could be said about totally disconnected groups in general, although important classes of such groups arising in number theory and as automorphism groups of graphs could be understood using techniques special to those classes. However, a complete general theory of these groups is now beginning to take shape following several breakthroughs in recent years. There is the exciting prospect that an understanding of totally disconnected groups matching that of the connected groups will be achieved in the next decade.