[Topology.beta] Friday DDT&G

[Rot, T.O.]

Happening in 20 mins!

From: "Rot, T.O." <t.o.rot at vu.nl>
Date: Friday, 1 April 2022 at 09:59
To: "_list_topology.beta" <topology.beta at listserver.vu.nl>
Cc: "Vorst, R.C.A.M. van der" <r.c.a.m.vander.vorst at vu.nl>, "Fabert, O." <o.fabert at vu.nl>, "Roos Hoefgeest, P.E.R." <p.e.r.rooshoefgeest at vu.nl>
Subject: Re: Friday DDT&G

Dear all,

This is happening today.
Best,
Thomas

From: "Rot, T.O." <t.o.rot at vu.nl>
Date: Tuesday, 29 March 2022 at 15:40
To: "_list_topology.beta" <topology.beta at listserver.vu.nl>
Cc: "Vorst, R.C.A.M. van der" <r.c.a.m.vander.vorst at vu.nl>, "Fabert, O." <o.fabert at vu.nl>, "Roos Hoefgeest, P.E.R." <p.e.r.rooshoefgeest at vu.nl>
Subject: Friday DDT&G

Dear all,

This friday there is the DDT&G. This starts at 14:00 in the union/intersection/mathlab. The speaker is Stefan Behrens about Freedman's disk embedding theorem and the topology of 4-manifolds.
Schedule

14:00-15:00: First part of the minicourse
15:30-16:30: Second part of the minicourse

Abstract

Freedman's disk embedding theorem is a cornerstone of 4-manifold topology. In order to appreciate the result, one has to be aware that manifold topology is divided into low and high dimensions. The border runs somewhere in dimension 4. The high dimensional world has powerful tools to tackle classification problems for manifolds, known as surgery theory and the s-cobordism theorem. A key feature of high dimensional manifolds is the Whitney trick, which allows to make certain geometric and algebraic intersection counts match. Unfortunately, the standard Whitney trick is not available in dimension 4 and it is known that the high-dimensional machinery does not apply to smooth 4-manifolds. In contrast, Freedman's theorem makes the Whitney trick available for a class of topological 4-manifolds (including all simply connected ones), thereby opening the gates for surgery and s-cobordism techniques. The goal of the minicourse is to explain the statement of the disk embedding theorem, to indicate why it is important, and to give at least a rough idea of the proof.

See this Quanta magazine article about the book Stefan coauthored about this topic.<https://www.quantamagazine.org/new-math-book-rescues-landmark-topology-proof-20210909/>

Bring your (master) students along!

We’ll have drinks afterwards. I will go out for dinner with the speaker to pizzalab. Let me know if you want to join asap.

Best,
Thomas
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