They can also be created or absorbed into something else. The mass of whatever absorbs them increases, and the mass of whatever is emitting them decreases when they do that.

The mass of everything is changing all the time. The thing that is constant is the rest mass.

[–] [email protected] 5 points 1 month ago

The object doesn't absorb their mass, but rather their energy (which admittedly can be equated to a mass via a factor of c^2, but that's not actually what's happening). The change in momentum that results from a photon hitting you isn't caused by a change in m, it comes from a change in v. If mass were the quantity being transferred, solar sails wouldn't work to move anything; they would just sit there and get more massive as photons hit them.

[–] [email protected] 3 points 1 month ago

That's how kamehamehas work, right?