A hypothetical particle postulated in supergravity theory to be the quantum of gravitational interaction, mediating the gravitational force. Like all force carriers, the graviton is a boson. It is presumed to have an indefinitely long lifetime, zero electric charge, a spin of 2, and zero rest mass (thus travelling at the speed of light). The graviton has never been detected. See also supersymmetry. See Table at subatomic particle.