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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?