 The weak force is next. If you recall, it's called the weak force because it only acts over an extremely short range, about 10 in the minus 18 meters. It happens to involve two exchange bosons, the W and Z bosons. These two, unlike the previous exchange bosons we learned about, have mass. Actually, they're pretty heavy, about a hundred times the mass of the proton. This is one of the reasons the weak force acts over such short ranges. Imagine how hard it must be to check huge bosons back and forth. The W boson can be positively or negatively charged, and we denote both types W plus and W minus respectively. The Z boson is uncharged. One good example of the weak force in action is in nuclear beta decay. Let's take a look a bit more closely at how beta decay works on the quark level. We'll choose neutron decay to focus on rather than look at the beta decay of the specific nucleus. Recall that the neutron consists of one up and two down quarks, while the proton is two up and one down quark. In the beta decay process, a down quark emits a W minus boson, causing it to transform into an up quark. The W minus boson then decays into an electron and an anti-electron neutrino, leading to the familiar beta decay products. The W and Z exchange particles were actually predicted by Sheldon, Glashow, Stephen Weinberg, and Abdus Selam in their electro-weak theory, which combined the electromagnetic and weak forces into one model. They won the Nobel Prize for this work in 1979. The W and Z bosons were discovered at CERN in 1983 by Carlo Rubia and Simon Van der Meer, who won the Nobel Prize for this work in 1984. I should note, Carlo Rubia and Simon Van der Meer won the Nobel Prize for this work, but there were actually quite a few people involved in this experiment. Now, we associated the weak forces range with the size of its associated exchange particles, but the strong forces also short range, and its exchange particle, the gluon, has no mass. So what's going on here? Well, the range of the strong force has to do with the fact that we never see isolated quarks in nature. The force keeping them together is indeed quite strong.