By the mid-1970s, scientists had grasped the basic idea that a proton consists of two up quarks and one down quark. As we have learned more, a more complex picture has emerged. We now know that the proton is actually a hot, bubbling cauldron of activity. Within this fascinating system, quarks and glue alike move at nearly light speed and quarks and anti-quarks pop continuously in and out of existence.

Much is still unknown about the proton. Why is it the size we observe? How does the intricate balance between the strong force and quark motion determine the proton's exact shape? Quarks and protons have a property called spin, but the spin of the quarks generates only 30% of the proton's spin. Where does the rest come from? The motion of the quarks? The spin of the glue?

The Jefferson Lab energy upgrade can help answer these questions.