A representation theorem for archimedean quadratic modules on *-rings

We present a new approach to noncommutative real algebraic geometry based on the representation theory of $C^{\ast }$-algebras. An important result in commutative real algebraic geometry is Jacobi’s representation theorem for archimedean quadratic modules on commutative rings, \cite[Theorem 5]{jacobi}. We show that this theorem is a consequence of the Gelfand-Naimark representation theorem for commutative $C^{\ast }$-algebras. A noncommutative version of Gelfand-Naimark theory was studied by I. Fujimoto. We use his results to generalize Jacobi’s theorem to associative rings with involution.