Physicists may have a brand-new way to measure the expansion rate of the universe — one of the biggest outstanding mysteries in cosmology — using space-time ripples predicted by Einstein.
A new study suggests that the faint gravitational wave background produced by numerous merging black holes across the universe can be used to independently measure how fast space is expanding. Even without detecting this background "hum" directly, the researchers show that it already places limits on the Hubble constant — a key quantity at the heart of one of modern cosmology's biggest puzzles.
