How does gravitational lensing reveal dark matter?

Gravitational lensing reveals the presence of dark matter by acting as a cosmic scale that measures mass through the bending of light.12

According to general relativity, massive objects warp space, causing light from background objects to deflect as it passes nearby. When astronomers observe distant galaxies or quasars, they often see these background objects distorted, stretched, or multiplied into multiple images by the gravitational influence of intervening mass.13

Because dark matter does not emit or reflect light, it remains invisible to traditional telescopes. However, by analyzing how this unseen mass distorts the shapes of background galaxies—a process known as weak lensing—astronomers can map the distribution of dark matter within galaxies and clusters. This method provides clear evidence that dark matter is a physical reality, as it allows scientists to detect mass that is gravitationally active but electromagnetically neutral.21