There is a whole lot of confusion around the concept of mass in physics.
The most common mistake is to confuse matter for mass as if the two things are the same. However, mass is merely a property of matter. It is not matter itself.
Matter is the physical stuff that we are made of. In a pure particle model of physics, photons and neutrinos are types of matter as well. We have protons and electrons which we can term ordinary matter, or matter in the open state, and then we have photons and neutrinos which we can refer to as the aether or matter in the closed state.
The fact that only matter in the open state has inertia has caused considerable confusion. Since many equate matter to mass, the conclusion has been that photons and neutrinos are not matter.
But photons and neutrinos are matter, just as much as protons and electrons. The fact that they have no inertia, and only photons react to gravity, does not take away their status as matter.
The big error that has been made ever since Newton’s days is to assume that the close link between gravity and inertia for ordinary matter is indicative of a single quality that joins the two things, and that this quality has to be a single phenomenon.
While it is true that the link between gravity and inertia is due to a single quality, it is not true that it is a single phenomenon.
The quality that joins gravity and inertia is charge. The more charged quanta a piece of matter consist of, the more it is affected by gravity, and the more time is required to change its energy when its constituent particle quanta are in the open state.
Proton, electron, photon and neutrino
- Protons are made up of thousands of charged quanta in the open state. They have much inertia and much gravity.
- Electrons are made up of three charged quanta in the open state, they have little inertia and little gravity.
- Photons are made up of six charged quanta in the closed state. They have no inertia and little gravity.
- Neutrinos are made up of a single neutral quantum in the closed state. They have no inertia and no gravity.
There is no mass as such. There is charged quanta, some in the open state and some in the closed state. Mass is merely a convenient, and very deceptive, shorthand for matter in the open state.