Around 1985, String Theory appeared unstoppable, yet it was coming apart from within.  Its defenders had worked out five apparently plausible versions of the theory, but these were not harmonious with each other.  Some worked with more dimensions; others had different types of strings, open or closed ones, or both at the same time.  Ten years would have to pass before the highly renowned physicist Edward Witten, of the Institute for Advanced Studies in Princeton, New Jersey, would give us M. Theory.  Witten had found a way to simplify the five theories into one, alleging that there were in fact not multiple theories but rather a wall of mirrors.  This theory gave us new concepts such as branas, membranes, open and closed strings, and a new dimension, which had to be added to the ten already existing ones.    

Most critics of string theories argue that because strings have still not been observed, due to their miniscule size, String Theory cannot be considered a theory of physics.  Rather, they allege, it is more appropriately a form of philosophical thought

Steven Weinberg, recipient of the Nobel Prize in physics for his role in the development of the Standard Model (current model), claims that no theory with such perfect and elegant mathematical foundations as String Theory could be an error.  It is inconceivable that so much elegance and beauty could be a waste.