Seminario G. Zavattini

Per il ciclo "Colloqui di Dipartimento" il giorno 20 Febbario alle ore 16 presso l'aula 412 il Prof. G. Zavattini (Universita' di Ferrara) terra un seminario dal titolo

The Quantum Vacuum: where nothing is actually something

Abstract

In the early nineteen-hundreds special relativity and quantum mechanics were discovered. One intrinsic consequence deriving from Einstein's energy-mass equation, Heisenberg's uncertainty principle and Dirac's relativistic equation of the electron is the zero-point energy leading to field fluctuations of both boson fields (e.g. photons) and fermion fields (e.g. electrons).
Together, the three discoveries revolutionised the idea of vacuum but also led to a series of fundamental problems: among others, the incompatibility of vacuum energy with measurements and the violation of the superposition principle in electrodynamics leading to light-by-light interaction and field dependent speed of light. In particular, in the presence of an external magnetic field, vacuum is predicted to behave as a birefringent crystal. This last quantum macroscopic effect stems from the 1935 nonlinear effective Lagrangian density for free electromagnetic fields by H. Euler and and B. Kockel. Due to its weakness, the effect is still awaiting a direct experimental confirmation: the induced birefringent due to an external magnetic field B perpendicular to the direction of propagation is An = 4x10-24 x B2 (with B in tesla). In the Department of Physics and Earth Sciences and INFN of Ferrara we built a polarimeter whose goal was to measure this tiny effect. Although the PVLAS experiment has set the present best limits on vacuum magnetic birefringence it missed the goal by less than a factor 10. The theme will be introduced, a description of the PVLAS experiment will be given and possible developments will be presented.