String theory

String theory, or superstring theory, is a class of models in theoretical physics which replace zero-dimensional points (particles) in four-dimensional spacetime with one-dimensional strings in a ten-dimensional spacetime as the fundamental building block of physics. The elusive goal is to develop a set of equations that unify all known natural forces (gravitational, electromagnetic, weak, and strong). A leading proponent of string theory has been Edward Witten of the Institute for Advanced Study.

There is much debate on whether string theory is truly scientific. Under the positivist philosophy, models must be falsifiable (i.e. it must be possible to define an experiment which will prove or disprove the theory) for them to qualify as science, and then they must survive these tests. In more general terms, a model is not scientific unless we can use it to make predictions about the world we observe, and it is consistent with those predictions. String theory has yet to yield a particular definitive test, or to produce any models that resemble any known particles or forces.