Astrophysics & Particle Physics-APPC 2026

Weak gravitational lensing is a sensitive cosmological method that detects minute distortion of the background galaxy shapes as their light traverses large-scale structures like galaxies, clusters, and dark matter halos. In contrast with strong gravitational lensing, which results in spectacular effects such as arcs and multiple images, weak lensing produces small, statistical changes in galaxy positions, demanding large sets of data and accurate measurements in order to identify them.This effect, also referred to as cosmic shear, offers direct proof for dark matter distribution, which is invisible but distorts spacetime in accordance with Einstein's theory of general relativity. By measuring the distortions in billions of galaxies, astronomers are able to make precise maps of the invisible mass that's structuring the universe.Weak gravitational lensing is also the most sensitive tool for measuring dark energy, the enigmatic force behind cosmic acceleration.

Since lensing maps out the evolution of cosmic structures throughout history, it can be used to test alternative models for cosmic expansion and make independent estimations of central cosmological parameters.Several major surveys including the Dark Energy Survey (DES), Kilo-Degree Survey (KiDS), Hyper Suprime-Cam Survey, and Euclid and Nancy Grace Roman Space Telescope missions soon to come are committed to measuring weak lensing to record precision. Combined with cosmic microwave background (CMB) and galaxy clustering observations, weak lensing is an important tool for constraining the standard cosmological model.The method is not without issues—systematic effects such as atmospheric distortions, telescope optics, and intrinsic galaxy alignment need to be properly corrected in order to produce reliable results.

Advances in machine learning, statistical methods, and deep-space observations are continually improving the precision of weak lensing studies.In summary, weak gravitational lensing is a cornerstone of modern observational cosmology. By tracking the faint imprints of cosmic structure on galaxy light, it provides vital insights into the nature of dark matter, dark energy, and the large-scale evolution of the universe.