If light has energy but no mass, how can it have momentum?
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Mass has momentum, but so does energy. In a way, mass and energy are kind of the same thing, or you could think of them as two different forms of the same thing.
Most things we deal with have lots of mass and are moving very slowly, so their momentum is almost entirely determined by their mass and velocity. You might be familiar with the equation *momentum = mass × velocity*. This is a pretty close approximation for most everyday things.
Some things, like light, have little or no mass and are moving very quickly, so their momentum is almost entirely determined by their energy and velocity. The equation for the momentum of light is a little too complicated to type neatly in Reddit, but you can see it at Wikipedia’s article on [mass in special relativity](https://en.wikipedia.org/wiki/Mass_in_special_relativity).
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