Astronomy
Measuring the Expansion Rate with Gravitational Lensing Time Delays
Quick fact
Gravitational lensing time delays can measure the Hubble constant with about 10% precision, offering an independent check on the expansion rate derived from supernovae and the cosmic microwave background.
Why this is interesting
You've probably seen the same star appear twice in a photo of a distant galaxy – but what if those twin images could tell us how fast the universe is expanding?