Truly impressive optical cavity. Today I was lucky to visit the European Gravity Observatory (VIRGO) just outside Pisa, Italy. The recent observation of a neutron star merger via gravity waves (of which VIRGO was a part) and via electromagnetic radiation has been a major development. Seeing the instrument used to detect gravity waves gave me a much better appreciation of the Herculean task this has been – the sensitivity is amazing. My host, Eric Genin, did a great job of showing me all of the complexities involved. There is a lovely demonstration interferometer in the entrance hall (picture above) that shows the operating principle of VIRGO, its ‘just’ a Michelson interferometer! Amazing to see how optical cavities can be used for such different things – creating new materials (Photmat), and detecting gravity waves (EGO). I was amused to see that during my visit, a period in which an upgrade is being carried out, the EGO was being used as a high-tech back drop for what looked like a fashion photo shoot.