Denote by XS1 the space of
all continuous maps from the circle into a simply connected finite CW complex, X.
Theorem: Let k be a field and suppose that either chark >dimX or that X
is k-formal. Then the betti numbers bq=dimHq(XS1;k) are uniformly
bounded above if and only if the k-algebra H∗(X;k) is generated by a single
cohomology class. Corollary: If, in addition, X is a smooth closed manifold and
k is as in the theorem, and if H∗(X;k) is not generated by a single class
then X has infinitely many distinct closed geodesics in any Riemannian
metric.