My Structure of Matter series has been on hold for a bit, as I have been debating how to describe protons and neutrons. These constituents of atomic nuclei, which, when combined with electrons, form atoms, are drawn in most cartoons of atoms as simple spheres. But not only are they much, much smaller than they are drawn in those cartoons, they hide within them a surprising commotion, one that cannot be anticipated from the relatively simple structures of atoms and of nuclei.
As I’ve described in my new article, along the lines of this short article and this more detailed one that I wrote some time ago in the context of the Large Hadron Collider, the story that scientists tell the public most often, that “a proton is made from two up quarks and a down quark”, is not in fact the full story — and in some ways it is deeply misleading. The structure of protons and neutrons is so entirely unfamiliar, and so complicated, that scientists neither have a simple way of calculating it, nor an entirely agreed-upon way to describe it to the public, or even to physics students. But I believe my way of describing it will be satisfactory to most particle physicists.
The new article is not entirely complete; it is perhaps only half its final length. I’ll be adding some further sections that cover some subtle issues. But since I suspect many people won’t feel the need to read those later sections, the completed part is written to stand on its own. If you like, take a look and let me know if you have questions, suggestions or corrections.