A proton is built from three valence quarks (two up quarks and one down quark), virtual gluons, and virtual (or sea) quarks and antiquarks (virtual particles do not influence the proton's quantum numbers). The ruling hypothesis was that since the proton is stable, it exists in the lowest possible energy level. Therefore, it was expected that the quark's wave function is the spherically symmetric s-wave with no spatial contribution to angular momentum. The proton is, like each of its quarks, a spin- ⁠ 1 / 2 ⁠ particle (a fermion). Therefore, it was hypothesized that two of the quarks would have their spins parallel and the third quark would have its spin antiparallel to that of the proton.