Oskar Klein (left) proposed in the 1920s that hidden spatial dimensions might influence observed physics. He poses with physicists George Uhlenbeck (middle) and Samuel Goudsmit in 1926 at the University of Leiden, the Netherlands.

AIP Emilio Segrè Visual Archives

I think sometimes the road begun existed before many of our own perspectives were added for considerations, so although we find that Einstein argue the simplicity and beauty of GR as it is, and rejected the quantum mechanical nature of the world, he did not reject the extensions of his thoughts to lead to other things. Some might of called this a mistake as well?

Kaluza and Klein showed in the 1920s that Maxwell’s equations can be derived by extending general relativity into five dimensions. This strategy of using higher dimensions to unify different forces is an active area of research in particle physics.

General consistancy of mathematics and numerical correlation, that unite, seem very plausible tools for recognition? Even if the mathematician, has divorced himself from the real world and said, it fits? Do they not become the Lewis Carroll’s and paint pretty pictures for us of a implausible world when they move into this abstract world of mathematics, without joining the physics? Einstein and Kaluza did this for us? There mathematics worked, and why not the Kaluza’s consideration to extra dimensions?

Let there be light! How could we not see that if the extra dimension was added how relevant might such unification have spoken to electromagnetism and gravity?

Kaluza-Klein theory is a model which unifies classical gravity and electromagnetism. It was discovered by the mathematician Theodor Kaluza that if general relativity is extended to a five-dimensional spacetime, the equations can be separated out into ordinary four-dimensional gravitation plus an extra set, which is equivalent to Maxwell’s equations for the electromagnetic field, plus an extra scalar field known as the “dilaton”

Thank you Wikipedia.

Einstein’s special relativity was developed along Kant’s line of thinking: things depend on the frame from which you make observations. However, there is one big difference. Instead of the absolute frame, Einstein introduced an extra dimension. Let us illustrate this using a CocaCola can. It appears like a circle if you look at it from the top, while it appears as a rectangle from the side. The real thing is a three-dimensional circular cylinder. While Kant was obsessed with the absoluteness of the real thing, Einstein was able to observe the importance of the extra dimension

Dialogos of Eide