Gravitons were first theorized by e=8 supergravity theory (which evolved from late supersymmetry theories and other attempts at Unification), and can be understood as a force-particle that represent gravitation , which is the ability to warp or bend space-time. Most cosmologists believed the graviton was an empty explaination at gravitation until the introduction of superstring theory, which was able to mathematically prove their existence instead of stronly relying on them as a basis for an otherwise sound theory. In superstring theory, gravitons are expressed as Spin-2 vector-bosons, which basically means that they are high spin force particles. See also quantum physics, Cosmology,Unification.