Mean curvature flow as a tool to study topology of 4-manifolds
  In this paper we will discuss how one may be able to use mean curvature flow to tackle some of the central problems in topology in 4-dimensions.   We will be concerned with smooth closed 4-manifolds that can be smoothly embedded as a hypersurface in R^5. We begin with explaining why all closed smooth homotopy spheres can be smoothly embedded. After that we discuss what happens to such a hypersurface under the mean curvature flow. If the hypersurface is in general or generic position before the flow starts, then we explain what singularities can occur under the flow and also why it can be assumed to be in generic position.   The mean curvature flow is the negative gradient flow of volume, so any hypersurface flows through hypersurfaces in the direction of steepest descent for volume and eventually becomes extinct in finite time. Before it becomes extinct, topological changes can occur as it goes through singularities. Thus, in some sense, the topology is encoded in the singularities. 
Tobias Holck Colding, William P. Minicozzi II and Erik Kjaer Pedersen
math.DG math.AP math.AT math.GT