“…There is a great deal of literature concerning the evolution of hypersurfaces by geometric heat equations in Euclidean space, particularly concerning evolution by mean curvature [Hu1,Hu2,W2,W3,HS1,HS2,HS3,SW,A7,CM,W1], but also including many other evolution equations in which the speed is a nonlinear function of the principal curvatures [T,C,Ge1,U,A1,A3,A4,HI,A5,AMZ,ALM]. There is an analogous situation for spacelike hypersurfaces in Minkowski space, and in particular the evolution of spacelike hypersurfaces by mean curvature flow has received considerable attention (see, e.g., [E1, E2, E3]); see also [Ge2,Ge3,Ge4], where spacelike hypersurfaces are deformed by inverse mean curvature flows in more general Lorenzian background spaces.…”