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.

The elementary particle that is associated with the force of gravity. In order to explain the relative weakness of gravity in relation to other forces, it has been proposed that gravitic fields exist in more than three spatial dimensions, and as such, are perceived as being weaker in our three dimensions.

Just to clarify: a graviton is actually a spin 2 tensor boson, not a vector. For deep reasons, a particle's spin relates directly to which irreducible representation of the Lorentz group it fits into (vectors, tensors, spinors, etc.). Here's a quick glossary:

Spin 0: Scalar

Spin 1/2: Spinor

Spin 1: Vector

Spin 2: Tensor

Particles higher than spin 2 cause problems in quantum field theory. However, they happen naturally in perturbative string theory. Some of us don't like string theory. Some do.

But yes, the graviton is associated with the gravitational force, which naturally is tensorial (consider the metric in general relativity). One can think of the graviton as a wave-like perturbation away from the flat Minkowski background. But then, don't we really want a background-free formulation of physics? I know I do.

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