A Geometric-Phase Timeline

Michael Berry

Global change without local change—a connecting idea in the physics of optical, quantum and other waves—has a multistranded history spanning two centuries.

figureA view near Skreen, in the west of Ireland, through a thin crystal sandwiched between crossed polarizers. The dark band across the interference fringes corresponds
to a geometric phase of π. [M. Berry]

Waves are central to our understanding of the physical world, and phase is the feature that distinguishes waves from classical particles. As waves evolve, their phases change, at rates that can themselves change when conditions change. In light, refracting materials or polarizers can change the phase; electromagnetic fields can change the phase of quantum charged particles; changing the depth of water can change the phase of waves on it.

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