In the subatomic world, nothing is simple. Take the proton, a fundamental particle found in the nucleus of every atom. For decades, students have been taught to picture the proton as a nice round ball, like a miniature planet. But no: The latest computer simulations show the particles can resemble peanuts, beehives, even bagels.


The three faces of a proton: sphere, peanut, and bagel.
Graphics courtesy of Gerald Miller/University of Washington (3).

Protons are complicated because they are composites of three smaller bits, called quarks, that zip around inside at roughly half the speed of light. "Quarks cannot escape from the proton. When they come to a wall, they turn around and change their direction," says theoretical physicist Gerald Miller of the University of Washington. Bouncing around gives the proton a net angular momentum. Using a mathematical model based on studies from particle accelerators, Miller showed how a proton's internal momentum affects its shape. Fast quarks that spin in the same direction as the overall proton distort it into a peanut, while quarks that have opposite spin breed bagels. Proton shape-shifting probably influences subatomic interactions in ways that are not yet known. Nobody understands exactly how the momentum inside a proton keeps changing. "All we can say is that sometimes it is large and sometimes small, and every proton can fluctuate instantly from one shape to another," Miller says.