Lattice Gauge Theory

The theory of how quarks and gluaons interact and build up hadrons is called quantum chromodynamics, QCD. Unluckily many of its predictions are extremely hard to calculate. The only reliable, systematic method is to approximate continous space-time by a four-dimensional lattice of points (with quark fields on the sites and gluon fields on the links) and to simulate the complete theory on a computer. Today we are thus able to realize the task, formulated by Feynman 35 years ago.

"Now we are in a position that's different in history than any other time in physics... We have theory, a complete and definite theory of all these hadrons, and we have an enormous number of experiments, and lots and lots of details, so why can't we test the theory right away, to find out whether it's right or wrong? Because what we have to do is to calculate the consequences of the theory. ...Well this time the difficulty is in the first step. If the theory is right, what should happen is very hard to find out. ...And therefore it's obvious, what my problem is - my problem is try to develop a way of getting numbers out of this theory, to test it really carefully, not just qualitatively, to see if it might give the right result."

R. Feynmann (1981)