Scale: 10^-15 meters = 1 fm = 1 femtometer

A Proton

There are 6 quarks that make up all the various hadrons (over 200 are known). In order of increasing energy -- and thus increasing mass -- the quarks are named up, down, strange, charm, bottom, and top. All the quarks have 1/2 integer spin -- and fractional electric charge.

So, how do you make a proton or a neutron out of fractionally charged quarks? Protons and neutrons are the lightest members of the baryon family of hadrons, and they are formed from a group of three quarks. (Mesons are a distinct family of hadrons constructed of one quark and one antiquark.) The proton is made from two up quarks and one down quark while the neutron is made from two down quarks and one up quark. Therefore the charge on a proton is (+2/3 +2/3 -1/3) = +1. The neutron's charge is (-1/3 -1/3 +2/3) = 0.

The image on this page is an artist's rendering of the interactions of the 3 quarks that make up the proton. It is similar in this respect to the images of the electron shells seen at 10^-10 and 10^-11. These images represent attempts to visualize objects that are too small to resolve with the highest energies currently possible.