THERE are many messy problems that physics does not attempt to solve. As the theorist Robert Jaffe of the Massachusetts Institute of Technology observed: we don鈥檛 try to predict the structure of a Volkswagen from first principles 鈥� but we like to think we could.
That鈥檚 why the current confusion about one of nature鈥檚 most basic particles, the proton, has touched a nerve. It is just the sort of problem that physics should master with aplomb. Yet neither theory nor experiment seems to be able to tell us with certainty either how big the proton is, or what makes it spin (see 鈥�Proton puzzle: Trouble at the heart of the atom鈥�). As we enter the era of the Large Hadron Collider, we are eagerly waiting to see whether the hoped for Higgs particle or hints of supersymmetry appear 鈥� or whether some totally unexpected finding will write the next chapter of particle physics. Our problems with the proton remind us that even supposedly settled science can challenge our presumptions of omniscience.
