The necessity to go beyond the standard model of particle physics and to understand quantum gravity has led to string theory. This ambitious attempt to unify all the forces of nature and all forms of matter as different vibrations of a string-like object is still in a pre-revolutionary stage. Although remarkable progress has been achieved in the last decade in understanding the perturbative and non-perturbative structure of string theory, we still lack a fundamental understanding of the theory. Many string theorists suspect that a profound conceptual change in our concept of space and time will be required for the final formulation of string theory.
