The space of spaces: curvature bounds and gradient flows on the space of   metric measure spaces
  Equipped with the L^2-distortion distance, the space "X" of all metric measure spaces (X,d,m) is proven to have nonnegative curvature in the sense of Alexandrov. Geodesics and tangent spaces are characterized in detail. Moreover, classes of semiconvex functionals and their gradient flows on "X" are presented. 
Karl-Theodor Sturm
math.MG math.AP math.DG