There is a 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 a property of matter. It’s not matter itself.

The nature of matter

Matter is the physical stuff that all things are made of.

We have inertial matter in the form of protons and electrons, and we have aethereal matter in the form of photons and neutrinos.

The fact that only inertial matter has measurable inertia has caused considerable confusion, because many equate matter to mass, and they conclude from this 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, doesn’t take away their status as matter.

The link between inertia and gravity

The error that has been made ever since Newton’s days is to assume that the close link between gravity and inertia is indicative of a single quality that joins the two, and that this quality has to be a single phenomenon, commonly referred to as mass.

But while it’s true that gravity and inertia are both due to a single quality, it’s not true that this quality is a single phenomenon.

Gravity is a force that acts on dielectric matter, and this force is proportional to the size of the subatomic particles that it acts upon.

Inertia is a time delay related to energy transfers between objects, and this time delay is also proportional to the size of subatomic particles.

Gravity and inertia have nothing in common except for their proportionality relative to matter.

Conclusion

Mass is an abstraction. It’s a convenient shorthand for inertia and gravity as they relate to matter, but mass doesn’t exist in nature. In nature, there’s only inertia and gravity. If anyone tries to find a physical thing called mass, they will find nothing.

Proton, electron, photon and neutrino