Discovered by Edwin Hubble and Georges Lemaître, the expansion of the universe is measured by two methods, and they yield different numbers: the ancient afterglow after the Big Bang gives 67 (km/s) for every 3.26 million light-years, while supernovae say 73. This "Hubble tension" hints at mysterious behavior of dark energy. Now the dispute has gained an independent referee — a combination of gravitational waves and gravitational lenses.
The referee compares two pieces of evidence. First — gravitational waves (ripples in spacetime, predicted by Rainer Weiss) from mergers of black holes and neutron stars. They reveal the distance to the cataclysm, much like the loudness of an echo reveals the distance to the sound source. Second — galaxy lenses, which bend the light of distant objects, creating multiple images with time delays. Combining distances from waves and delays from lenses yielded 84 (km/s) over the same interval, but with a 14% margin of error — the main snag being the distribution of dark matter inside the lenses. The first simultaneous detection of waves and light happened only in 2017, and now such events are caught nearly every week; the most distant recorded signal came from 9 billion light-years away. A couple of years of observations — and the referee will deliver a final verdict on the nature of dark energy.
🎯 The idea of using gravitational waves to measure cosmic distances was proposed in 1986 by [scientist:Rainer Weiss]Rainer Weiss[/scientist], but the first real event with "sound" and light was captured only 31 years later, in 2017.
🎬 In science fiction, gravitational lenses are often portrayed as natural telescopes peering into the past. In the novel "Light of Distant Stars," astronomers use them to glimpse the edge of the universe.