Strong gravitational lensing is a powerful and mature technique for probing galaxies and the Universe as a whole. In the past twenty years, strong lensing observations have enabled to carry out unique studies, such as measurements of the dark matter distribution in galaxies and galaxy clusters, detections of substructure in galaxies, measurements of the expansion rate of the Universe with time-delay lenses, and high-resolution analyses of strongly-lensed high-redshift galaxies. While these efforts have improved our understanding of galaxy evolution and cosmology, there are still open questions that strong lensing observations can help to address. What is the nature of dark matter and dark energy? Is the history of the Universe well described by a flat lambda cold dark matter model? The answers to these questions have profound fundamental physics implications.

The field of strong lensing is about to be revolutionised by the advent of new observational facilities, such as Euclid, the Rubin Observatory, the Roman Space Telescope and the Chinese Space Station Telescope (CSST). These telescopes and their associated surveys will lead to the discovery of around 100000 new strong lenses, an increase of more than two orders of magnitude with respect to the current sample size of confirmed lenses. Such a large amount of data gives us the potential for carrying out strong lensing studies with very high precision. At the same time, however, it poses new challenges: to fully take advantage of this improvement in precision, it is necessary for the accuracy of the models used to interpret these data to improve as well. Furthermore, traditional analysis methods, based on the detailed study of a few select systems, do not scale well to very large sample sizes. With this symposium, we aim to bring together observational and theoretical members of the community to review the progress of the field and develop a roadmap for the new era of strong gravitational lensing.

The proposed symposium date of June 2023 is auspicious as it precedes the expected first data release from flagship survey facilities. In the past few years, many new astronomers have entered the field, started groups and introduced fresh and innovative ideas. State-of-the-art techniques have been developed to resolve structure in the early Universe, test the nature of dark matter, test fundamental physics and efficiently analyse forthcoming big data sets, demonstrating that the strong lensing community is well-placed to address critical scientific questions in astrophysics. The goals of the symposium are

  • to understand the preparedness of the community to analyse and adapt to forthcoming big data;
  • to assess the progress of the field in regard to precision lens modelling and modelling of high-angular-resolution data, and to understand what developments are needed;
  • to find synergies between observations and simulations of dark matter and the high-redshift Universe;
  • to determine the scientific questions that strong lensing will address over the next decade and foster collaboration.