Astronomy Colloquium

Ordinary baryonic particles (such as protons and neutrons) account for only one-sixth of the total matter in the Universe. The remainder is a mysterious "dark matter" component, which does not interact via the electromagnetic force and thus neither emits nor reflects light. However, it has the usual gravitational signature, and gravitational evidence for it is mounting. The past seven years have seen dramatic progress in measurements of weak gravitational lensing, the slight deflection of light from distant sources due to the curvature of intervening space. Recent observations from the Hubble Space Telescope have provided direct proof for, and large-scale maps of dark matter in the Universe. I review the current state of the art and prospects/challenges for the future of the field. Indeed, gravitational lensing provides one of the most promising routes to fulfil the astrophysical end of the deal in a larger quest to determine the nature of dark matter.