Dimension in physics

I have a solid understanding of topological dimension. I heard that some string theororists think that the universe is >= 10-dimensional, but that the extra 7+ dimensions are too small for us to encounter. How can a dimension be small; is it just a model for what is observed, or is it based in theory?

>>11
If you can get yourself a PhD in research for a specific field, then you're set for life, pretty much. 

Me.. I'm going into high energy physics.  I just have to try not to let education and learning blur out reality.  I still want to get laid. ;_;