 Myers's theorem

For a connected Riemannian manifold of dimension $n\ge 2$, assume geodesic completeness and $\mathrm{Ric}\ge (n-1)\kappa g$ for a constant $\kappa >0$. The Riemannian distance then has diameter at most $\pi /\sqrt{\kappa }$; the manifold is compact and its fundamental group is finite. The dimension restriction excludes the vacuous one-dimensional Ricci bound.

Myers's theorem is a result in Riemannian geometry, which concerns the relationship between the geometry of a complete Riemannian manifold and its topology. Specifically, the theorem states that if \( M \) is a complete Riemannian manifold that has non-negative Ricci curvature, then \( M \) can be isometrically embedded into a Euclidean space of a certain dimension.