Twelve particles and four forces are all we need to explain everything in the known world.
But the fact that all the properties of a force can be determined by knowing the symmetries is one of the most important discoveries of twentieth-century physics. This idea is what is meant by the gauge principle.2
Even as the first string theorists faced formidable obstacles, they could inspire themselves by thinking about all the puzzles that would be solved if elementary particles were vibrations of strings. It is a pretty impressive list: 1. String theory gave us an automatic unification of all the elementary particles, and it also unified the forces with one another. All come from vibrations of one fundamental kind of object. 2. String theory automatically gave us gauge fields, which are responsible for electromagnetism and the nuclear forces. These naturally arise from the vibrations of open strings....
of geometries that succeed one another in time is not.
Note: the graphic history of the world expressed in quantum gravity terms