While this may seem like a silly question, I had difficulty answering it completely. "If space is a vacuum, why aren't we somewhere else already?" If it is truly empty, devoid of any substance or mechanism whereby it might restrain or compell the action of an entity, what keeps entities apart? If "inertia" is the answer, from whence is inertia derived? What permits acceleration to accuumulate for a given object and an object's motion at one location to be passed on to that of the same object at another location--is it a property of that object, a property of space, or both?