Hello, i try to find some opinions on these points a) If a brane action in a bulk is defined, in that case, that a brane is modelwise moving through a bulk, how is this ratio defined? Is this a regular "velocity" in that meaning, that space is being passed in a period of time? b) If a 4D-Einstein-Spacetime is chosen, where space itself is a slice cut through spacetime, how can the ratio, with which the space is moving through time, be defined? I suppose a "space per time" fails due to it is more a "time per X", but what is X? Thanks in advance for answers.