User:Boris Tsirelson/Sandbox1

Well, this is an interesting... what? physics, not chemistry.

Fortunately or unfortunately, I am not a chemist, nor a physicist; thus I am not entitled to draw the border between chemistry and physics. However, all this exchange about mass only convinces me that the problem, what is mass, and what has mass, is deeply physical, far not chemical. The same can be said about the problem, what is space and what does it mean, to occupy space. And therefore the definition that says "occupies space and has mass", be it apt or not, is anyway inappropriate for chemistry. For "matter (physics)" — maybe; for "matter (chemistry)" — not at all.

Naively or not, I still believe that chemistry is about regrouping atoms in molecules. Thus, atoms and molecules are directly relevant; and everything else is relevant as far as it influences the process of regrouping atoms in molecules. Accordingly, the relevance of the photon mass (if any) to chemistry is as small as this very mass is.