I have seen in many places, for example here, the statement that the proton consists of valence quarks and sea quarks. I am somewhat confused as to where this picture comes from. The sea quarks are virtual quark-antiquark pairs. I have encountered virtual particles only in the context of perturbation theory. Is this where the idea for the sea quarks is coming from? I find this strange, because the proton is a bound state and it should not be possible to describe it by using perturbation theory. Also, perturbative approaches to QCD only work at high energy. I know that in lattice QCD they sometimes take into account the sea quarks. This puzzles me even more, since LQCD is advertised as non-perturbative. So how do the virtual particles arise there. I tried to see what they do in LQCD. First of all, the action is replaced, for example, by the Wilson action. Secondly, in the path integral formalism the quark fields are integrated out (in the continuum case) and a fermion determinant remains in the expression for the expectation value. However, this matrix is quite tedious, so they use some tricks to reintroduce the quark fields back into the action. Setting the determinant equal to one corresponds to neglecting the sea quarks. But I'm still lost about how virtual particles enter into the LQCD. Finally, shouldn't there also be all the other particles "inside the proton"? I mean virtual photons, electrons, and even W & Z, not just virtual quarks. To me the "old picture" of the proton with only three quarks, which interact through the gluon fields, is clearer than trying to include an infinite amount (?) of all kinds of virtual particles. All the peculiarities of the system can be buried into the gluon fields, right? That's where the sea quarks originate in the first place. Any thoughts?