Well, maybe. String theory, which does show a good deal of promise in being able to explain a lot of things, has this tiny little hitch that it only works if there are the extra dimensions Glom referred to. The reason proposed for why we don't notice them is that they might be really, really small ("compactified" is the term used). There is an effort to actually detect these directly (for example, looking for deviations from the inverse square law of gravity at very short ranges), but so far there's been no confirmation. So I'd personally leave the eleven-dimensional universe in the category of "promising theory" rather than consider it well established fact.