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Poincare conjecture

  1. May 30, 2012 #1
    I've been doing a project on Henri Poincare and I am attempting to explain his conjecture to my Calculus class so I am using the common lower dimensional equivalent to do so. If a rubber band is wrapped around an object and becomes smaller and smaller until it is a point than that object is homeomorphic to a sphere and contrast this with the case of a torus.

    My problem is that I am confused as to whether the Poincare conjecture involves wrapping a one dimensional line around a four dimensional figure or if it is a two dimensional plane around a four dimensional figure. I am only briefly mentioning this so the answer shouldn't be too complex.
  2. jcsd
  3. May 31, 2012 #2


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    you want a 1 dimensional line. The 3 sphere though is a 3 dimensional manifold - meaning that locally it looks exactly like a small region in three dimensional space.

    Not every rubber band will shrink to a point by itself. It may need a little nudge. This can be seen on the regular sphere. Stretch a rubber band on it that forms a great circle. It will sit tight until without moving until you push it slightly. Then it will shrink to a point.
  4. Jun 2, 2012 #3
    Thank you that was very helpful!
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