About 40 years ago when I was 15 my science teacher would occasionally collar me in the hallway and bellow, "What is matter". Now, I have a pretty good laypersons grasp of atomic structure and particle physics, yet when I ponder the question, I find I still cannot really answer the question in any meaningful way, and I suspect that neither can anyone else. Prove me wrong. What I mean is that when the lay person thinks of atoms they imagine some tiny little hard round billiard ball like object because matter seems to be made of solid stuff. But the cognoscenti understand that it is merely electric repulsion and the exclusion principle which gives an appearance of solidity. Yet still there is this stuff all around me and the question remains, what precisely is it. The protons seem to be where all the real action is with regards to mass, but even mass is a bit mysterious, apparently no one really knows what mass is other than the effect it has. And the proton is really just a trio of quarks which are confined in a tiny space. And the quarks themselves do not have much mass, and 'stuff' doesn't seem to be 'mass', so matter isn't really mass. So we are back to 'what is matter'. Well what is a quark, is it anything other than it's effect on the universe. It can be measured, sure, but what precisely is it. I've heard particles described as nothing more than a disturbance in a field, a field of what? Is the field then matter? Heisenberg wanted to do away completely with any notion of trying to visualise particles. So is matter just a mathematical concept? It seems that if it's not a hard little ball of something then it's just some sort of a concept in someone's mind, but if that is the case what is all this stuff I see around me? That's not a concept, or is it. So this is where I now am, 40 years later still wondering about the question, 'what is matter'.