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SUMMARY:Dave Gabai
DTSTART:20210503T190000Z
DTEND:20210503T200000Z
DTSTAMP:20260423T005721Z
UID:mitgt/17
DESCRIPTION:Title: <a href="https://researchseminars.org/talk/mitgt/17/">K
 notted 3-balls in the 4-sphere</a>\nby Dave Gabai as part of MIT Geometry 
 and Topology Seminar\n\n\nAbstract\nWe give examples of codimension-1 knot
 ting in the 4-sphere\, i.e. there are 3-balls B_1 with boundary the standa
 rd 2-sphere\, which are not isotopic rel boundary to the standard 3-ball B
 _0. In fact isotopy classes of such balls form a group which is infinitely
  generated. The existence of knotted balls implies that there exists inequ
 ivalent fiberings of the unknot in the 4-sphere\, in contrast to the situa
 tion in dimension-3. Also\, that there exists diffeomorphisms of S^1 x B^3
  homotopic rel boundary to the identity\, but not isotopic rel boundary to
  the identity.  (Joint work with Ryan Budney)\n
LOCATION:https://researchseminars.org/talk/mitgt/17/
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