We can measure the fine structure constant with very great precision, but so far none of our theories has provided an explanation of its measured value. One of the aims of superstring theory is to predict this quantity precisely. Any theory that could do that would be taken very seriously indeed as a potential 'Theory of Everything'.
John D. Barrow, Impossibility: The Limits of Science and the Science of Limits
constants-of-nature, fine-structure-constant, physics, string-theory