I can picture gravity as the warping of spacetime as postulated by GR but I have not heard a descriptive explanation of how a graviton might cause an attraction between two masses, or even if it is a cause in quantum theory. So okay, you have a closed string or a massless particle with a spin of 2 out there, but how does that cause the earth to fall towards the sun, for example? Is it some kind of a messenger particle that, when it hits something, says in effect "come this way?" What is the function of this theoretical particle and what role does it play in gravitational attraction? All I have heard are descriptions of the particle itself, as opposed to how it acts.