University of Bristol physics professor Sir Michael Berry visited the University of Wisconsin on Monday to for a seminar on geometric phase. The seminar was part of the Chemistry Department’s Willard Seminar on physics given yearly. Berry will be giving two additional lectures on Tuesday and Wednesday.

Berry won the Lorentz medal in 2014, a prize which is given out every four years by the Royal Netherlands Academy of Arts and Science and is one of the most prestigious honors in theoretical physics.

Berry’s talk focused on the mathematics, applications of and history of geometric phase. Geometric phase is a change that occurs in waves like photons or other particles. It describes the relatively slow changes that occur in the waves, which exhibit distortion when recombined. Berry gave two real-world examples of these phenomenon that illustrate the idea with images familiar to most people — the Foucault pendulum, or a simple pendulum with a ball and chain, and a cat landing on its feet.

For both of these actions, the changes are minute but result in the item that is acted upon returning to a slightly different position from which it originated. For the pendulum, the rocking motion is cyclical, but the rotation of the Earth beneath the pendulum moves it ever so slightly compared to the table it is swinging above.

With a cat dropped with its back to the floor, Berry explained its change in terms of preserving angular momentum. The cat begins with no angular momentum, must end with no angular momentum, but must change its orientation to land on its feet, Berry said. To do this, the cat could contort itself into a “c” shape, rotate the ends of the “c” equally in opposite directions, but turn itself onto its feet while having never changed the energy in its system.

“[A cat] does because she deforms her body,” Berry said, “She’s not a rigid body, in a cycling of the space of shapes where at the end she has pretty much the same, not exactly the same shape at the beginning, but she has turned.”

Berry was the first person to generalize the description of phase change across systems in 1984. His continued work in the field has pushed forward the integration of fields of physics and chemistry.

Berry’s next two seminars will focus on four geometrical-optics illusions on Tuesday and quantum chaology on Wednesday. They will be held in 1315 Seminar Hall in the Chemistry Building.