Hi all, I began to read this paper :http://www.physics.adelaide.edu.au/mathphysics/abstracts/ADP-95-11-M28.html" On page 9 the author foliates spacetime into spatial hypersurfaces, [tex] \Sigma_t [/tex], labeled by a global time function, t. for each point of [tex] \Sigma^t [/tex] there is a vector [tex]n_\mu[/tex] orthogonal to it These vectors generate a flow on spacetime. Physically what are these curves? are they geodesics? Have you links using his notations for the intrinsic metric? thanks.