Does light have momentum?

In my opinion it is not necessary to evoke the theory of relativity or quantum physics to explain how light can have momentum but not mass. In the 19th century, it was already known that light can collide with matter; a beam of light can set a small wheel (in vacuum) rotating. read more

When light bounces off an object it does impart momentum to it. In the simplest case, light bouncing off a very massive stationary object, the light imparts no energy to the object. The momentum imparted is twice that of the incoming light, since it just changes directions and thus changes the sign of its momentum. read more

"momentum is the product of mass and velocity, so, by this definition, massless photons cannot have momentum" This reasoning does not hold. Momentum is the product of energy and velocity. read more

Footnote: Note that this answer uses only classical physics. It does not use ideas from relativity or quantum mechanics at all. Those subjects are completely unnecessary for determining whether light has momentum. Light would have momentum even if we lived in a non-quantum, non-relativistic world. read more