These failed predictions as well the embarrassment of an infinite number of string-theory solutions have engendered a growing skepticism about string theory among many leading physicists. As the Nobel Prize–winning theoretical physicist Gerard ’t Hooft has explained: I would not even be prepared to call string theory a “theory,” rather a “model,” or not even that: just a hunch. After all, a theory should come with instructions on how . . . to identify the things one wishes to describe, in our case, the elementary particles, and one should, at least in principle, be able to formulate the rules
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