String theory is a very interesting topic. Our Physical Science is based on two different sets of mathematical equations one for mass another for energy. One of its primary assumption in these equations is independently Mass Or Energy is indestructible ( can neither be created nor destroyed) . But Einstein broke this assumption in E= MC2, where mass and energy can be transformed to each other. But still we cannot explain physical property of mass or energy with single set of mathematical equation. Here comes the string theory, where it tells if a sting is allowed to vibrate freely then the mathematical equation it will follows in the vibration, that can be used to unify all these independent equations which we are using for explaining physical world of mass and energy. But no one could find yet this sub atomic string in physical world, so the assumption is one day it will be discovered.