If gravity is not a force, why does it need to be carried by Gravitons?

[Soumya_M]

According to General Relativity, gravity is not a force. It arises from the curvature of space-time due to presence of matter. Matter curves space-time in a way that the paths of things appear to be bent giving rise to th effects of gravitiation.

But if gravity is not a force, why do we need gravitons to carry it?

 

[zhermes]

That's an excellent question, and one which isn't entirely answered.

General Relativity (GR) per se does not predict that their would exist such a particle; quantum field theories however imply the existence of such a particle---largely as a symmetry of nature. Once you really get into the nitty-gritty of particle physics, there are analogies begging to be made between GR and the other "3" forces. For instance, you can understand electromagnetism in terms of curvature of the electromagnetic field OR you can understand it in terms of the exchange of photons between charged objects.

There are lots of little hints that a graviton should exist (for instance, both from quantum field theory and from some generalizations of GR you would expect such a particle to have spin 2). But it is not for certain.