The essence of string theory is a literal assertion: Elementary particles—electrons, photons, quarks, and their numerous cousins—are not pointlike objects but “strings” of energy forming tiny, wiggly loops. If a stringy loop vibrates one way, it manifests itself as an electron. If it shimmies some other way, it looks like a quark. Wacky as this idea may sound, there are good reasons why physicists so fervently embraced it. Smolin, the more elegant writer, is far better at conveying the conceptual import of physical theorizing with a minimum of technical detail. Neither book, though, is easy reading for the uninitiated.
To put it very briefly, what turned interest in string theory from an oddball enthusiasm to a mainstream occupation was a twofold realization that came in 1984. That’s when two of the early string pioneers, John Schwarz of Caltech and Michael Green, who was based in London, published a paper showing that just a handful of possible string theories were free of mathematical inconsistencies that plagued traditional particle-based models, and also had sufficient capacity (the number and variety of internal vibrations, roughly speaking) to accommodate all the known elementary particles and their interactions. There was one little difficulty: The systems these theories described existed only in 10 dimensions.
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