Zero mass but non-zero weight

twisting circle by Dave Whyte

Photons have zero rest mass but non-zero weight.

There is a tutorial paper on this by M.B. van der Mark and G.W. ‘t Hooft titled “Light is heavy“.

Physicists do not use the term “rest mass” anymore. More appropriate term is “invariant mass”. Masses of elementary particles are invariant but their weight (related to their total energy) changes of course.

Photons have no mass but they have energy. This is the reason why gravitational field of the stars bend the photons passing by (gravitational lensing). Remember, according to the General Relativity theory (which has been tested numerous times) gravitational attraction is based on the total energy-momentum, not on mass.

There is a grey area. The mass of the Higgs boson is 125 Gev (in energy units). What is the weight of the Higgs boson? I have not seen any clear explanation of the relationship between the Higgs field and the gravitational field.