a non-expert question !! hi From what i understand , the number of spacetime dimensions needed by strings theory to be consistent arises due to the quantization of the classical action of the string , given that there shouldn't be tachyonic states in the mass spectrum of the theory . my question goes like this : why don't physicists look for a new quantization process that gives 4 dimensions , and looks like the known quantization when the string shrinks to a point particle , so that Q.M is modified for the sake of strings theory , but remains correct for our classical picture where particles are point like objects . in other words : strings theory modifies G.R by adding some corrections to einstein-hilbert action - right ??- that leave the action intact for large scales , but it doesn't seem to do the same when it comes to quantum mechanics !!! it certainly says a lot about QFT , but QM is a given in the formulation of strings theory !!! excuse my technical terms , i'm not an expert , i just have an interest in the subject .