Hi, I am new of this forum. I am thinking about electromagnetic mass. Considering the mass where the neutron is a composite particle of proton and electron. from etherealmatters.org/article/mass-electromagnetic-force It is known that there are two kinds of masses. It is an inertial mass and a gravitational mass. The equivalence principle is that both are the same. The matter that make up are electrons, protons, and neutrons. Neutron is electron + proton, so let's think about electrons and proton…