Strings

String Theory is one of the most intriguing theories put forward. They came into being coz the QFT that is the quantum field theory was insufficient. The case of Insufficiency is the unification of all the four basic forces. These are Electromagnetic, Weak ,Strong and Gravity.

The fact is it has been possible to unify both electromagnetic and weak forces and resulted in Electroweak force. Theoritically even Strong force can be approached from this direction. But when it comes to Gravity this is not the case. Here some of you might know that gravitons are the basic particle of gravity. (The basic theory for gravity is still the general theory of relativity put forward by Einstein.) So applying QFT to GR results in so intangible results. Basically it is that the force between two gravitons become infinity. "Dont ask me what are this". I didnt do the maths for this.

Enter the string, here all the particles are only different modes of vibration of the string including the graviton. Thus strings are the fundamental building blocks of everything. The strings might me closed or open these are the variation in the string theories put forward till date that the string might be closed or open. When they are closed it traces a sheet as it moves through time and a tube when it is open. So, the first great achievement of String Theory was to give a consistent theory of quantum gravity, which resembles GR at macroscopic distances.

Bringing supersymmetry into this picture gives you superstrings. That is initially the string theory was applied to only bosons as i understand it. That is particles having integer spin. Later when it started being applied to the fermions we get superstrings. Thus supersymmetry.