Anti Dam - choose a jigsaw puzzle to solve

In theories of quantum gravity , the graviton is the hypothetical elementary particle that mediates the force of gravity . There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity . In string theory , believed to be a consistent theory of quantum gravity , the graviton is a massless state of a fundamental string . If it exists, the graviton is expected to be massless because the gravitational force is very long range and appears to propagate at the speed of light , and a spin-2 boson because the source of gravitation is the stress– energy tensor, a second -order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four -current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation , because a massless spin-2 field would couple to the stress– energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered , it must be the graviton.