From string to superstring theory
June 20, 2009 Leave a comment
This is basic introducing to superstring theory. In string theory we assume string as fundamental building block. These string can be closed loops or open. As string moves through time it traces tube or sheet according to whether closed or open. Well, there string are free to vibrate in different vibrational mode similar to what you see in a general string in your physics lab. These different vibrational modes represent the different particles of different spins. In that way there is mode describing the graviton ,the particle responsible for the force of gravity, having two spin quantum number. The point is that we can make sense of the interaction of the graviton in string theory in a way that we could not in QFT . The first great achievement of this theory was to give a consistent theory of quantum gravity which resembles GR At macroscopic distance. As well as this theory also have the necessary degrees of freedom to describe the other interactions. The particles are classified according to spin into boson(with integer spin like graviton) and fermions which have off half integer spin. The boson particle carry forces while fermions is used to make matter which we see around us. By introducing supersymmetry to original string theory we obtain superstring theory which deals with both matter and forces. There are three sting theory, two of them based on closed string and another one is based on open strings. We obtain two more string theory by mixing up these theories , known as heterotic string theory.