Capturing targetspace dynamics on the worldsheet

General facts about string theory:

• Both kinematics and dynamics of the space-time follow from some simple properties of 2D sigma-model

• The target space of this sigma-model is identified with the space-time; the space-times fields, such as gravity, are identified with the coupling constants of the sigma-model

• The “simple properties” can be either classical or quantum or both; in any case, they should imply the equations of motion of the space-time fields

• String theory predicts the existence of the infinite tower of massive particles, with the mass of the order Planck scale, which are essentially unobservable experimentally