a way that is almost uniquely specified by mathematical self-consistency, forming an apparently valid quantum theory of gravity. Since its birth as the dual resonance model which described the strongly interacting hadrons as strings, the term string theory has changed to include any of a group of related superstring theories and larger frameworks such as M-theory, which unite them. A shared property of all these theories is the holographic principle. String theorists have not yet completely described these theories, nor have they determined if these theories relate to the physical universe or how.[1] The logical coherence of the approach, however, and the fact that string theory can include all older theories of physics, have led many physicists to believe that such a connection is possible. In particular, string theory is the first candidate theory of everything, a way to describe all the known natural forces (gravitational, electromagnetic, weak and strong) and matter (quarks and leptons) in a mathematically complete system. On the other hand, many detractors criticise string theory because it has not yet provided experimentally testable predictions. Like any other quantum theory of gravity, it is widely believed that testing the theory experimentally would be prohibitively expensive, requiring heroic feats of engineering on a solar-system scale. Although string theory, like any other scientific theory, is falsifiable in principle, critics maintain that it is unfalsifiable for the foreseeable future, and so should not be called science. Work on string theory is made interesting because of the mathematics involved, and because of the large number of forms that the theories can take. String theory strongly suggests that spacetime has eleven dimensions [2], not the usual three space and one time; but the theory can easily describe universes with four observable spacetime dimensions too.[3] String theories include objects more general than strings, called branes. These are black-holes charged with a differential form vector potential which has more than one index, a different type of electricity and magnetism where the fundamental objects are extended. By studying certain p-branes and identifying them with D-branes, endpoints for strings, certain types of string theory are shown to be equivalent to certain types of more traditional gauge theory. Research on this equivalence has led to new insights on quantum chromodynamics, the fundamental theory of the strong nuclear force We live in a wonderfully complex universe, and we are curious about it by nature. Time and again we have wondered--- why are we here? Where did we and the world come from? What is the world made of? It is our privilege to live in a time when enormous progress has been made towards finding some of the answers. String theory is our most recent attempt to answer the last (and part of the second) question. So, what is the world made of? Ordinary matter is made of atoms, which are in turn made of just three basic components: electrons whirling around a nucleus compo