This will, no doubt, sound like a silly question but I am just getting my feet wet in string theory. It seems from what I know so far, that string theory is very far removed from our observable universe. What I mean by that statement is that it seems we just say "well, maybe our universe is a brane within a larger space" or "maybe the extra-dimensions are just compactly curled up in very small radii." A few years ago, when I knew even less, I sort of intuited what string theory might consist of if I had to invent it myself. I wanted to actually start out with our observable 4-dim Minkowski space (curved or un-curved) and then attach at bundle structure to the manifold where the strings evolved. That way, what we see as a point evolving in the base-space (our universe) is actually a string evolving in the bundle space of some dimension. Furthermore, the image of the string evolution in the bundle will be the worldsheet I think. The one problem I see immediately is that in this formulation, closed strings would still project onto our universe which I don't think is a good thing. This seems to me to be a much more sensible starting point given that it makes explicit where the observable world is in the larger picture...but I'm not so arrogant as to think there's any sense to it! So why doesn't motivating the theory like this work? Thanks for any help!