A question about the first $$L^2$$-Betti number

In a recent arXiv preprint (arxiv:2106.15750) J. A. Hillman discusses a new homological approach towards some old results on 3-manifold groups due to Elkalla. In his article he runs into an interesting question concerning the first $$L^2$$-Betti number of finitely generated groups: Assume that a finitely generated group G has infinite subgroups $$N\leq U$$ such … Continue reading "A question about the first $$L^2$$-Betti number"

Computer assisted verification of contemporary mathematics

Half a year ago Steffen Kionke wrote a blog post on condensed mathematics wherein he mentioned that Peter Scholze put up a challenge to formally verify a key fundamental result of a joint paper with Clausen: a result Scholze terms his most important theorem to date. Today I want to inform you that the mentioned … Continue reading "Computer assisted verification of contemporary mathematics"

A hyperbolic 5-manifold which fibres over the circle and subgroups of hyperbolic groups

Recently appeared a highly interesting paper by Italiano, Martelli, Migliorini on the arXiv (2105.14795) (Okay, this was already three weeks ago – I don’t follow the “geometric topology” – and someone had to point me there). The paper solves at least two longstanding open problems by studying an explicit 5-dimensional hyperbolic manifold. It is well-known … Continue reading "A hyperbolic 5-manifold which fibres over the circle and subgroups of hyperbolic groups"

GDM-Monat 2021 – Vortrag zur Doppelten Diskontinuität

Auf dem GDM-Monat im März 2021 (voriger Beitrag dazu: link) hörte ich auch den Vortrag von Viktor Isaev zu dem Thema: Entwicklungsverläufe von Studierenden bezüglich ihrer Wahrnehmung zur doppelten Diskontinuität. Was diese Doppelte Diskontinuität ist, erklärt man am besten mit folgendem Zitat von Felix Klein: Der junge Student sieht sich am Beginn seines Studiums vor … Continue reading "GDM-Monat 2021 – Vortrag zur Doppelten Diskontinuität"

Singmaster’s conjecture

Singmaster’s conjecture is an easy to state conjecture about Pascal’s triangle. It is easy to see that every natural number in Pascal’s triangle occurs only a finite number of times. The conjecture of Singmaster now claims that there is actually a global upper bound on this number of occurrences! The highest number of occurrences currently … Continue reading "Singmaster’s conjecture"

GDM-Monat 2021 – Hauptvortrag zum Mathematischen Beweisen

Die Gesellschaft für Didaktik der Mathematik (GDM) hat wegen der Corona-Pandemie anstatt einer Präsenztagung im Jahre 2021 im März einen Monat lang Vorträge und Veranstaltungen ‘dezentral und online’ durchgeführt (link). In manche der Vorträge hatte ich damals reingehört (hauptsächlich solche, die sich mit der Hochschuldidaktik beschäftigen) und wollte auf diesem Blog kurz über die Inhalte … Continue reading "GDM-Monat 2021 – Hauptvortrag zum Mathematischen Beweisen"

Shaw Prize 2021

The Shaw Prize 2021 in the Mathematical Sciences goes to Jean-Michel Bismut and Jeff Cheeger for their remarkable insights that have transformed, and continue to transform, modern geometry. Bismut […] imported ideas from probability into index theory, reproving all the main theorems and vastly extending them, which enabled him to link index theory to other parts … Continue reading "Shaw Prize 2021"

Characterizing Euclidean 3-space

In my previous post about the recent preprint of Jiang Wang we saw the following characterization of Euclidean 3-space among all contractible 3-manifolds: It is the only one that admits a complete Riemannian metric of non-negative scalar curvature. Today a preprint was posted on the arXiv:2105.09035 by Bargagnati and Frigerio providing another characterization: The only … Continue reading "Characterizing Euclidean 3-space"