Well, it turns out that Einstein and Kaluza and many others worked on trying to refine this framework and apply it to the physics of the universe as was understood at the time, and, in detail, it didn't work.
Acontece que Einstein, Kaluza  e muitos outros trabalharam na tentativa  de refinar esta infraestrutura e aplicá-la à física do universo tal como era compreendida  naquela altura, e não funcionou.