String Theory or Field Theory ? 1

The status of string theory is reviewed, and major recent developments-especially those in going beyond perturbation theory in the string theory and quantum field theory frameworks-are discussed. This analysis helps better understand the role and place of string theory in the modern picture of the physical world. Even though quantum field theory describes a wide range of experimental phenomena, it is emphasized that there are some insurmountable problems inherent in it-notably the impossibility to formulate the quantum theory of gravity on its basis-which prevent it from being a fundamental physical theory of the world of microscopic distances. It is this task, the creation of such a theory, which string theory, currently far from completion, is expected to solve. In spite of its somewhat vague current form, string theory has already led to a number of serious results and greatly contributed to progress in the understanding of quantum field theory. It is these developments which are our concern in this review.