What did Anne Green say about gravitational lensing as evidence for dark matter?

Anne Green of the University of Nottingham called gravitational lensing some of the nicest evidence for dark matter. Einstein's general relativity says mass bends space, so a massive galaxy cluster bends the light of a galaxy far behind it into multiple distorted arcs. Mapping those arcs shows how mass is spread out, and it reveals large lumps of dark matter surrounding the visible galaxies, the halos that simulations predicted.

• Strong lensing needs a very heavy object, such as a big galaxy cluster, lined up with a distant galaxy.
• Lensing shows not only that dark matter is there but where it is distributed.

▸In their words

“You can consider space like a rubber sheet.” Anne Green · at 23:41 — open in the transcript →

Source: our own transcription of the episode. The full conversation is on In Our Time (2026-10-26). Read the whole episode summary →

▸More from this episode