What is the hypothetical particle that mediates gravity?

The hypothetical particle that mediates gravity is the graviton.

In quantum field theory, forces are described through fields and their associated particles. The photon mediates electromagnetism, gluons mediate the strong interaction, and W and Z bosons mediate the weak interaction. Physicists therefore expect a quantum description of gravity to involve a corresponding messenger particle: the graviton.

A graviton is predicted to be electrically neutral, massless, and a boson with spin 2. Its masslessness would explain gravity’s effectively unlimited range, while its spin-2 character distinguishes it from the spin-1 photon. In general relativity, gravity is instead described as the curvature of spacetime, so the graviton belongs to proposed quantum-gravity theories rather than established experimental physics.

No individual graviton has been detected, and no complete, experimentally confirmed quantum theory of gravity exists. Gravitational waves have been observed, but detecting those waves is not the same as detecting their hypothetical quantum particles. The term “graviton” was introduced in 1934, while Albert Einstein had discussed quantized gravitational radiation as early as 1916.