What is a Photon?

A photon is a quantum particle of light and is the carrier of the electromagnetic force. Before the 20th century it was always believed that light was a wave. However, several experiments and theories have now shown us that light is also a particle which contains no mass. We now know that light consists of massless particles known as photons. Photons are not thought to be made up of smaller particles and are a basic unit nature called an elementary particle. The mass of a photon is zero and it always moves at the speed of light in a vacuum.