Once you know that light is the standard for measuring length and time, you might wonder whether light itself has weight. Light is both a wave and a particle. How much do you suppose such particles (photons) weigh? The answer is: photons have no mass. Photons are particles with zero mass, no electrical charge and a spin (rotation) value of 1. They can travel far because they weigh nothing. In quantum mechanics, photons are thought to mediate electromagnetic force. Although photons have no mass, there are extraordinary cases in which light, specifically evanescent light, clings to extremely small objects, behaving as if it had mass.