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Type I string theory
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<p>In <a href="/facts/Theoretical_physics/Cs2Y12rQ">theoretical physics</a>, type I string theory is one of five consistent supersymmetric <a href="/facts/String_theory/HUJFIPYH">string theories</a> in ten dimensions. It is the only one whose strings are unoriented (both orientations of a string are equivalent) and the only one which perturbatively contains not only <a href="/facts/Closed_string/3EtMw6n2">closed strings</a>, but also <a href="/facts/Open_string_(physics)/3EtMw6n2">open strings</a>. The terminology of type I and <a href="/facts/Type_II_string_theory/CUEmEtr3">type II</a> was coined by <a href="/facts/John_Henry_Schwarz/mmjLJe5S">John Henry Schwarz</a> in 1982 to classify the three string theories known at the time. </p>