The Banach-Tarski paradox, monsters and their gentler cousins

27.01.2022 15:00 - 15:45

Y. Lodha (U Wien)

The Banach-Tarski paradox is one of the most striking and counterintuitive phenomena in all of mathematics. Von Neumann's study of the paradox led to the formulation of the so called von Neumann-Day problem, which has been attributed to Mahlon Day from the 1950s. The problem was solved in the late 70s by the construction of various finitely generated "monster" groups. However, I will explain how elementary tools from descriptive set theory recently led to the construction of considerably "less scary" new solutions, some of which are finitely presented (and even type \(F_{\infty}\)).



Zoom Meeting