A quantum particle of light is a photon, which is a particle of light that has both wave-like and particle-like properties. Photons are the smallest unit of light and are the basic building blocks of all other forms of electromagnetic radiation, such as radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. Photons have no mass and travel at the speed of light. They are also the carriers of the electromagnetic force, which is one of the four fundamental forces of nature.