"The underlying physical principle behind string theory is unknown"
As an architect I found an interesting form solution: "transformable rigid single- or compounding rings" formed by 4x mutual hinged quarter rings, called strings. Only one particle for the multiverse.
see: https://vixra.org/author/leo_vuyk
Now the new Mathematics behind this system including rotation hinges, should be discovered, which seems to be not easy according to professor G.'t Hooft.( Uni-Utrecht)
Now the new Mathematics behind this system including rotation hinges, should be discovered, which seems to be not easy according to professor G.'t Hooft.( Uni-Utrecht)
The system: 
