lol. First of all, what is gravity? a force that pulls mass relatively based on other mass. Why? Science doesn know. How? Theorists theorize that gravity is made up of gravitons, and these particles act on the mass of another object, but these particle are yet unfound and unfounded. Ok if gravitons pull on mass, as opposed to pther mass then these theoretical gravitons must be made from or attracted to mass. So then how does an object get mass? Theorists theorized that the higgs boson, the 'god particle', traveled through a higgs field and like magic a particle is bestowed a particular amount of mass, that is acted upon by gravtions thus creating gravity. The problem with that is the higgs field has NOT been found, and the higgs boson, which was found in 2012, turns out to have NOT BEEN FOUND in 2014.
So now we don know anything about gravity, mass or where these two fundamental elements of nature arise from and how they work. Gravitons, the higgs boson, and the higgs field are all theoretical objects and most likely do not exist. thus gravity is as big a question now as it was to issac newton a couple hundred years ago. Go science!