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Soul Theorem




:If (''M'',''g'') is a Complete ''non''- Compact Riemannian Manifold with Sectional Curvature K\ge 0, then (''M'',''g'') has a Compact Totally Convex , Totally Geodesic Submanifold ''S'' such that ''M'' is diffeomorphic to the Normal Bundle of ''S''.

The submanifold ''S'' above is called a soul of (''M'', ''g''); it is not uniquely determined, but any two souls are isometric.

The theorem was proved by Jeff Cheeger and Detlef Gromoll , as a generalization of an earlier result of Gromoll and Wolfgang Meyer .


SOUL CONJECTURE


In the same paper Cheeger and Gromoll gave the following conjecture:

:Suppose ''M'' is complete and noncompact with sectional curvature K\ge 0, but K > 0 at some point. Then soul of ''M'' has to be a point (or equivalently ''M'' is diffeomorphic to {\mathbb R}^n).

The conjecture was open for about 20 years, and was solved by Grigori Perelman with a surprisingly short argument.


REFERENCES


  • Cheeger, Jeff; Gromoll, Detlef On the structure of complete manifolds of nonnegative curvature. Ann. of Math. (2) 96 (1972), 413--443.

  • Gromoll, Detlef; Meyer, Wolfgang On complete open manifolds of positive curvature. Ann. of Math. (2) 90 1969 75--90.

  • Perelman, G. Proof of the soul conjecture of Cheeger and Gromoll. J. Differential Geom. 40 (1994), no. 1, 209--212.