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4.7 Unification of natural forces
According to the imagination of the elementary particles physicists, all natural forces were, at the Planck time, combined in a single force.
A mathematical model for the unification of all known natural forces (electromagnetic, weak, strong and gravitational interaction) is believed found by means of the Super string theory  [17], p. 220:
„The Super string theory leads us back to the origin of time, when all cosmic forces were completely symmetrical and presented one primary super force.“
According to the Super string theory, the first symmetry fractioning separating the gravitation as the first force from the remaining natural forces, took place at the Planck time, when the universe was about  10 - 43 seconds old.
By later symmetry fractionings, the other natural forces then also became independent ( see Fig. 7)

Fig. 7: "Freezing“ of the natural forces by symmetry fractioning

In 1968, the theorists Weinberg, Salom and Glashow were able to unify the electromagnetic and the weak force into the electro weak force, on the basis of a calibration symmetry, - the Yang-Mills Theory. Since then, no major progress could be achieved.
In 1984 only, the unification of all natural forces received new impetus, when a super string model presented by Green and Schwarz featured enough symmetry to eliminate certain anomalies of earlier string theories.
But even these were not able to lead to a breakthrough. [33], p. 225:
“One knows now that there are thousands of string theories which mathematically are just as consistent as the two Green- Schwarz theories. Which string theory and if one of them at all is capable to serve as a model for describing the real world, we do not know until today. Thus, the unification of all natural forces further on belongs to the big unsolved riddles in theoretical physics.”
 
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