Volumes that remain Euclidean in the small still swell or shrink once they travel along geodesics; the single tensor that records that average distortion is Ricci curvature. Ricci isolated the contraction from the full Riemann tensor around 1900. In coordinates it is the trace R_{ij}=R^k_{ikj}, and it already contains enough geometric information to decide whether nearby volumes expand or collapse. When the metric itself is set in motion by ∂g_{ij}/∂t=-2R_{ij}, the same quantity that measures bending becomes the force that smooths it. The resulting Ricci flow turns an instantaneous snapshot of curvature into a dynamical process that can dissolve singularities and reveal hidden topology.

Volunteers for the Changchun 2027 Winter Universiade send greetings in different languages. Take a test and find out what they're saying! The Games will be held in Changchun, northeast China’s Jilin, from Jan 15 to 25, 2027, presenting a spectacular feast of winter sports to audiences.