## SISSA Colloquium: Geometric phases and the separation of the world

The waves that describe systems in quantum physics can carry information about how their environment has been altered, for example by forces acting on them. This effect, known as the geometric phase, will be at the centre of the *Colloquium* held by Michael Berry of the University of Bristol on **Wednesday 6 November**. The geometric phase also occurs in the optics of polarised light, where it goes back to the 1830s, and it gives insight into the spin-statistics relation for identical quantum particles. The underlying mathematics is geometric: the phenomenon of parallel transport, which also explains how falling cats land on their feet, and why parking a car in a narrow space is difficult. Incorporating the back-reaction of the geometric phase on the dynamics of the changing environment exposes the unsolved problem of how strictly a system can be separated from a slowly-varying environment, and involves different mathematics: divergent infinite series.

The *Colloquium *will take place in the P. Budinich Main Lecture Hall at **4 pm**.

(Image M. Berry)