This is a very interesting subject. I woke up tonight (as I'm wont to do) with Einstein's (Was it his?) thought experiment about bowling balls and marbles on a trampolene surface to show the bending of spacetime. I may have taken the analogy a little far, but I suddenly have a problem...I imagined the experiment with a somewhat more elastic surface (perhaps). If we have a marble, say, that has a very high mass, but a small radius (some super dense material) this would cause a deep curve with a small radius  where as a beach ball would produce a shallow dent with a wide radius. For the two to be attracted, then the event horizons of the two curves need to come into contact with each other. So this leads to several questions (that woke me up):
1Is gravity, being a curvature of spacetime as opposed to Newtonian force, of equal density itself or does size affect the curvature as well as mass?
2 Is the flexability of the "surface" (spacetime) constant thoughout the universe or is it more apt to curve in some places tha others?
3 Is the "flexability" such that what I suggested (in my apparant dream) impossible in our universe.
4 Is it possible for a super dense object to bend spacetime completely around itself  would we know? Maybe this would just be its own little universe/dimension???
