This is a page I created at wikipedia. It has been threatened with removal from wikipedia so I am placing a copy here. It needs to be adapted to this wiki. In our personal human experiences, we seem to exist in a universe with three spatial dimensions. Some theories in physics, including string theory, include the idea that there are additional spatial dimensions. Such theories suggest that there may be a specific number of spatial dimensions such as 10. The question, "Why 10 dimensions?" arises from these theories.