Can bent gravitational waves measure the universe's expansion rate?

Massive black holes that merge can have their gravitational waves bent by intervening matter, like light through a lens. This team shows that future space detectors (Taiji and LISA working together) can use these lensed signals to measure how fast the universe expands—a number cosmologists still argue about. Combining just five such events yields precision comparable to current gold-standard methods, without requiring independent distance measurements.