Gravitational Lensing of Waves: a new window into cosmology and fundamental physics

Gravitational lensing, the bending of light by gravity, is essential for interpreting astronomical observations and provides key insight into astrophysics, cosmology, and fundamental physics. A new frontier in gravitational lensing intersects with another key prediction of Einstein’s theory: gravitational waves, fluctuations of space-time produced by the collision of black holes and neutron stars. Like light, gravitational waves are deflected and magnified by the intervening matter distribution, but their unique properties (low frequency, lack of absorption and ab-initio emission models) enable novel signatures and applications. I will present the phenomenology of lensed gravitational waves and the science they will deliver to 1) identify high-redshift sources, 2) constrain dark matter on small scales and 3) probe the association between black hole mergers and supermassive black holes in galactic nucleii. Current facilities have the potential to discover lensed gravitational waves by the end of this decade, with abundant detections expected by upcoming instruments on the ground and in space.