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.
Bem, acontece que Einstein e Kaluza e muitos outros trabalharam em tentar refinar essa grade e aplicá-la à física do universo como era entendido àquele tempo e em detalhe ela não funcionou.