Abstract: Our Universe is still largely a mystery. Elusive dark matter shapes cosmic structures, while the Universe expands at a rate that we struggle to understand. Unraveling these fundamental open questions demands a deeper look into the distant cosmos, where gravitational waves from stellar-mass binary black holes offer a unique observational window.

Unlike electromagnetic signals, gravitational waves traverse the Universe without alteration, except for gravitational lensing. Their long wavelengths make them subject to diffraction by cosmic structures, providing an unprecedented opportunity to map dark matter and test the foundations of gravity. If we can recover these lensed signals, we gain a cosmic magnifying glass to observe the most distant black hole mergers and illuminate their origins. Current gravitational-wave observations have already produced puzzling lensing candidates (e.g., GW231123), and the first definitive detections are expected very soon.

In this talk, I will explain why gravitational-wave lensing is uniquely informative, outline how deep‑learning methods can accelerate its discovery, and show what the first detections could reveal about dark‑matter substructure and astrophysical black hole formation channels.

This seminar is part of the “Holography in the Gravitational Wave Era” (HOLOGW) project, with Grant Agreement n. 1011419092, funded by the European Union / ERC.