Mapping the dark Universe with gravitational weak lensing

Gravitational lensing is a fascinating phenomenon that happens because of the way gravity works according to Einstein’s theory of General Relativity: mass curves spacetime. Imagine you have a massive object, like a star or a galaxy, sitting in space. This object has a strong gravitational pull, which means it will bend spacetime and – since light follows a path along this now bent space – it also bends the path of light that passes nearby.