Light is composed of photons, which have no mass, so therefore light has no mass and can't weigh anything. Not so fast. Because photons have energy -- and, as Einstein taught us, energy is equal to the mass of a body, multiplied by the speed of light squared.
Answers & Comments
In addition to being a particle, light is also a wave.
This allows it to carry momentum, and therefore energy, without having mass.
Answer:
Light is composed of photons, which have no mass, so therefore light has no mass and can't weigh anything. Not so fast. Because photons have energy -- and, as Einstein taught us, energy is equal to the mass of a body, multiplied by the speed of light squared.