# String Reference Libraries

String Theory -- A string theory is a physical model whose fundamental building blocks are extended objects (strings, membranes and higher-dimensional objects) rather than points. String theories are able to avoid problems, such as infinite energy density, associated with the presence of mathematical points in a physical theory. The term 'string theory' properly refers to both the 26...

M-Theory -- 'M-Theory' is the name of the unknown theory of everything which would combine all five Superstring theories and the Supergravity at 11 dimensions together. The theory requires mathematical tools which have yet to be invented in order to be fully understood. The theory was proposed by Edward Witten. The following article is somewhat technical in nature, see M-theory...

- The navel or umbilicus.
- In Greek archaeology: A central boss, as on a shield, a bowl, etc.
- A sacred stone in the temple of Apollo at Delphi, believed by the Greeks to mark the 'navel' or exact center-point of the earth.