original: string theory is a developing branch of theoretical physics that combines quantum mechanics and general relativity into a quantum theory of gravity .
simplifications: string theory is a developing branch of theoretical physics that combines quantum mechanics and general relativity into a quantum theory of gravity . it has quantum mechanics . string theory is a developing branch of theoretical physics that combines general relativity into a quantum theory of gravity string theory is a developing branch of theoretical physics that makes quantum mechanics and general relativity into a quantum theory of gravity . string theory is a branch of theoretical physics that combines quantum mechanics and general relativity into a quantum theory of gravity . string theory is a new branch of theoretical physics that combines quantum mechanics and general relativity into a theory of quantum gravity . string theory is a developing branch of theoretical physics , that combines quantum mechanics and general relativity into a quantum theory of gravity . string theory is a developing branch of theoretical physics -lrb- involving only the theory and not the practical session -rrb- that combines quantum mechanics and general relativity into a quantum theory of gravity . string theory is a developing branch of theoretical physics that combines quantum mechanics and general relativity into a quantum theory of gravity .