Graviton
| Composition | Elementary particle |
|---|---|
| Statistics | Bose–Einstein statistics |
| Interactions | Gravitation |
| Status | Theoretical |
| Symbol | G |
| Antiparticle | Self |
| Theorized | 1930s The name is attributed to Dmitrii Blokhintsev and F. M. Gal'perin in 1934 |
| Mass | 0 |
| Mean lifetime | Stable |
| Electric charge | 0 e |
| Spin | 2 |
In theoretical physics, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory.
If it exists, the graviton is expected to be massless (because the gravitational force appears to have unlimited range) and must be a spin-2 boson. A spin-2 particle is also known as a tensor boson, compared to a spin-0 scalar boson and spin-1 vector boson. The spin follows from the fact that the source of gravitation is the stress–energy tensor, a second-order tensor (compared to 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. As the graviton is hypothetical, its discovery would unite quantum theory with gravity. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.
There is no complete theory of gravitons due to an outstanding mathematical problem with renormalization. This problem has been a major motivation for models beyond quantum field theory, such as string theory.
The three other known forces of nature are mediated by elementary particles: electromagnetism by the photon, the strong interaction by the gluons, and the weak interaction by the W and Z bosons. The hypothesis is that the gravitational interaction is likewise mediated by an – as yet undiscovered – elementary particle, dubbed as the graviton. In the classical limit, the theory would reduce to general relativity and conform to Newton's law of gravitation in the weak-field limit.
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