Gravity cannot be exchanged by photons or any other spin 1 particle, for that matter. Spin 1 particles lead to repulsive forces for like charged particles. Thi

Gravity cannot be exchanged by photons or any other spin 1 particle, for that matter. Spin 1 particles lead to repulsive forces for like charged particles. This leaves you with spin 0 and spin 2 as the simplest alternatives. Spin 0 doesn't result in light bending and gives a wrong result for Mercury's perihelion precession. Spin 2 gives you General Relativity.