why not

"Entered string theory to rectify the problem."？

或

"Enters string theory to rectify the problem."？

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String theory, which nowadays dominates the research programmes and main funding of theoretical physics in many western universities (at a recent conference in Cambridge some 440 of them gathered to discuss their subject), was not so much discovered as invented in order to solve a vexing explanatory deficit. In the early 1970s, physicists announced the so-called “standard model” — a theory that seeks agreement between the contrasting realms of super-huge objects, such as stars and planets, (known as relativity) and the super-small realms of the subatomic (known as quantum). The standard model, however, failed to explain gravity. Enter string theory to rectify the problem. In its simplest terms, this complex set of notions claims 10 or 11 space dimensions (as opposed to the three of everyday human perception), and assumes a “landscape” of myriad elementary bundles of energy (strings) that interface not only with the universe we inhabit but a multiplicity of unseen and unknowable parallel universes.
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