On November 2/3, the PIER-funded workshop on QED vacuum birefringence took place at DESY.

The workshop gathered experts working with optical lasers, X-rays and even the LHC, who are set out to measure how photons interact with their own kind through so called `vacuum electron loops'. This incredibly weak interaction, which is there even for visible wavelengths, is manifest in physics but its measurement remains a challenging task even 80years after its first prediction by W. Heisenberg and his student H. Euler. Approximately 40 scientists from around the globe attended the workshop which focused very much on the exchange of ideas through allowing for long discussions after each presentation.

A main goal of the workshop was to assess if such a measurement might be possible at the ALPS-II experiment. In this experiment, also scientists from Hamburg university and DESY are building an instrument to test new physics models and maybe, thanks to the workshop,
also the previously untested prediction of this photon interaction.

The workshop also comprised a public talk by Prof. Holger Gies of Jena University and the Helmholtz Institute Jena: Approximately 140 interested laymen were guided along pictures of corn fields and water through some basic physical theory to understand why physicists
are so much determined to use light-self-interactions to test our understanding of quantum theory and maybe even find novel physics on the way.