SUPERSTRING THEORY : ORIGINS

The hunt for String Theory started in the late 1960s in an attempt to understand the strong nuclear force. This is the force that is responsible for holding protons and neutrons together inside the nucleus of an atom as well as quarks together inside the protons and neutrons. A theory based on fundamental one dimensional extended objects, called strings, rather than point-like particles, can account qualitatively for various features of the strong nuclear force and the strongly interacting particles (or hadrons). The basic idea in the description of the strong interactions is that specific particles correspond to specific oscillation modes (or quantum states) of the string or energy. This proposal gives a very satisfying unified picture in that it postulates a single fundamental object (namely, the string) to explain the nature of different observed hadrons.
However in the early 1970s another theory of the strong nuclear force –called quantum chromodynamics (or QCD) –was developed. As a result of this, as well as various technical problems in the string theory approach, string theory became less interesting than before. The current viewpoint is that this program makes good sense of the basic viewpoint of science, and so it has again become an active area of research. The concrete string theory that describes the strong interaction is still not known, though one now has a much better understanding of how to approach the problem. String theory turned out to be well suited for an even more ambitious purpose: the construction of a quantum theory that unifies the description of gravity and the other fundamental forces of nature. In principle, it has the potential to provide a complete understanding of particle physics and of cosmology.