, ну, вот один из ответов: It's not yet fully "approved", mainly because of the fact that not all of the mathematics are yet discovered. It's basically like any theory, you stick with it for as long as it can explain real-world phenomena. It's the same for superstring theory. Superstring theory is (thougt to be) able to bridge the gap between Einsteins Relativity theory and Quantum Mechanics. Both of these theories are widely accepted, but the funny thing is that they are mutually exclusive! Meaning: they cannot both be right! Relativity Theory is right in the world of really massive and large things (stars, planets, galaxies) while Quantum Mechanics is right in the world of really small things (particles). Unfortunately, these theories have conflicting ways of explaining the world. Superstring theory is (as of yet) the answer to this "gap", but because it hasn't been fully developed yet it's not fully accepted.
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