[AGarvin]

Hi fellas,

There is really only one viable theory of gravity and that's Einsteins General Theory of Relativity, which says that space curves in the presence of mass. The greater the mass, the greater the curvature. The "ball on rubber sheet" analogy is a sometimes confusing way it illustrate this concept.

Also, one of the underlying concepts of GR is the principle of equivalence, that is, being in a gravitation field, such as standing on the surface of the earth, is equivalent to uniform acceleration. Based on this, gravity is like rolling down a hill of space. The greater the mass, the steeper the hill gets the closer you get to the "bottom" (ie, the source) and the faster you go.

The idea of the graviton comes from Quantum Mechanics. In QM, everything has to be quantised. Just as the photon is a quanta of electromagnetic radiation and the gluon is a quanta of the strong nuclear force, so to gravity must be quantised. Under this theory, gravity would be the exchange of gravitons between masses.

Unfortunately, the mathematics of both theories fall apart trying to explain this, GR at small scales around the Planck length, and QM just all over.

Cheers,
Andrew.