The structure of the nucleon

We have known for years that the nucleon must have a finite size. In the 1950s, with the development of quantitative calculational techniques in quantum electrodynamics, there were many attempts to describe the size of the nucleon, but none was successful. The advent of quark physics and the demonstration through high‐energy deep inelastic scattering of electrons by nucleons that there are three objects in the central nucleon core, and that these objects behave at high energies as if they are free and massless, gave impetus to a new description of nucleonic structure. Ever since Hendrik A. Lorentz's work on the theory of the electron, we have been trying to give elementary particles finite sizes to make their self energy finite. Whereas Lorentz introduced rods to hold his extended electron together (the method did not work), we now believe that the vacuum exerts a pressure on the “bubbles,” or “bags,” that we have to make to allow quarks to exist, and that this pressure keeps the bubbles from expanding. As the drawings in figure 1 and on the cover of this issue indicate, we can think of the nucleon as three colored quarks in such a bubble, surrounded by a cloud of mesons.