The string theory entails the existance of additional dimensions ,up to 11
In the past also Kaluza postulated the existance of a fourth spatial dimension
Thanks to this extra dimensions he was able to unify the equations of the elettromagnetic and gravitational field as well as to explain the existance of neutral and electrically charged particles
The unification was the Einstein's dream so he took this theory very seriously
It is not a laughable theory but as a matter of fact it is not supported by any experimental evidence