Graviton

This article is about the hypothetical particle. For other uses, see Graviton (disambiguation).
Graviton
CompositionElementary particle
StatisticsBose–Einstein statistics
Familyspin-2 boson
InteractionsGravitation
StatusHypothetical
SymbolG[1]
Theorized1930s[2]
The name is attributed to Dmitrii Blokhintsev and F. M. Gal'perin in 1934[3]
Mass0
< 6×10−32 eV/c2 [4]
Mean lifetimestable
Electric charge0 e
Color chargeNo
Spin2 ħ

In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity. In string theory, believed by some 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 has a very long range, and appears to propagate at the speed of light. The graviton must be 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 gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.[5]

  1. ^ G is used to avoid confusion with gluons (symbol g)
  2. ^ Rovelli, C. (2001). "Notes for a brief history of quantum gravity". arXiv:gr-qc/0006061.
  3. ^ Blokhintsev, D. I.; Gal'perin, F. M. (1934). "Гипотеза нейтрино и закон сохранения энергии" [Neutrino hypothesis and conservation of energy]. Pod Znamenem Marxisma (in Russian). 6: 147–157. ISBN 978-5-04-008956-7.
  4. ^ Zyla, P.; et al. (Particle Data Group) (2020). "Review of Particle Physics: Gauge and Higgs bosons" (PDF). Progress of Theoretical and Experimental Physics. Archived (PDF) from the original on 2020-09-30.
  5. ^ For a comparison of the geometric derivation and the (non-geometric) spin-2 field derivation of general relativity, refer to box 18.1 (and also 17.2.5) of Misner, C. W.; Thorne, K. S.; Wheeler, J. A. (1973). Gravitation. W. H. Freeman. ISBN 0-7167-0344-0.