# Gunther Cornelissen: Let’s twist again

**Time: **
Wed 2020-02-19 15.15 - 16.15

**Lecturer: **
Gunther Cornelissen, Utrecht University

**Location: **
Oskar Klein, AlbaNova

### Schedule

15:15-16:15 Colloquium lecture by Gunther Cornelissen in Room Oskar Klein, AlbaNova

16:15-17:00 SMC social get together with refreshments

### Abstract

All our “physical observations” correspond to spectra of operators. But do spectra determine uniquely the underlying (geometric) structure? This problem of Bochner became well known through Bers’ formulation “Can you hear the shape of a drum?” (used as title for a famous article of Kac), and the answer is “no” in general. Sunada gave a general method of construction of isospectral, non-isometric manifolds based on a group theoretical construction that number theorists had come up with in the 1930’s. I will discuss the history of the problem and indicate how one can sometimes use more group theory to construct twisted Laplacians whose spectrum does determine the isometry class. Joint work with Nobert Peyerimhoff (Durham).