String Theory

String theory started as a simple way of modelling the characteristics of elementary particles as the result wave movement on a tiny circular string so that the various quantum states that produce particles are dependant on
the number of standing waves around this string.  So more massive particles with more energy had more nodes in the waves thus more waves around the string.

Circular "String" showing wave

Going back from this, the idea came from an electromagnetic representation of a particle as a photon going in a circle trapped by its own self gravity. So a photon pair when collided can form a little circulating standing wave and the electrical energy so contained makes for a gravitational bending of space so that the photon travels in a circle, when there is only one wavelength round a particle is formed in its ground state and thus lowest mass, higher energy states occur with more waves and thus higher frequency. The relationship of the trapped energy to frequency gives Planck's constant. It is discontinuous because only some combinations of wavelength to circular path and gravitational curvature fit.

I originally discussed this with Jonathan Dostrovski in about 1967-1968, he thought straight strings with mass and tension was easier to calculate, hence "string theory", when we were both working at the Rutherford Laboratory, Oxford.