Photons have no mass. Yet they interact gravitationally, as all energy does, with other energetic and massive particles. This means that if you put multiple photons in a system, you get something that appears to have mass, even though none of the constituent particles do have mass.
That makes me wonder:
Is mass really a fundamental part of reality? Couldn't it be that massive particles (protons/neutrons/electrons) are just composed of massless particles like photons knotted up, confined to a small area and whizzing around in very tight orbits? So everything is, in a sense, massless?
The search for and discovery of the Higgs Boson suggests to me, in my limited understanding, that scientists believe mass is a fundamental property that some particles have. And also that mass is fundamentally different than other types of energy (though conversion is possible). Does all of this preclude a system like I describe?