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Macroscopically, the forces are electromagnetism and gravity.  In previous posts, I had noted down how an electromagnetic potential fits adapted to a hypersurface of S4 and one can see how the geometry of S4 naturally gives us the duality between electric and magnetic fields.  The Ricci curvature of the submanifold automatically contains a ‘cosmological constant’ term which happens to be quantitatively close to the measured value.  There is the essence of the unification of these two forces but additionally we can see how electromagnetism would not be a genuine $U(1)$ gauge theory which can be used for experimental tests of S4 theory.  At each point of the ‘physical hypersurface’ the normal geodesic is a circle of fixed radius but the total space is not that of a bundle as there can be intersections.
The ‘maximally parsimonious’ grand unification possible for a scaled S4 boils down to the fact that the scaling factor of $1/h$ simultaneously produces the right quantization and produces the right cosmological constant and unification of electromagnetism and gravity is fairly simple.  Compare this simplicity of an almost classical grand unification to the complexities of string theories.