13,8 billion years ago, the universe was just born. In its first moments, it expanded incredibly fast. This period was named inflation (super-fast stretching). The idea was proposed by Alan Guth. Quantum tremors in space stretched out and turned into a shudder — gravitational waves. Their existence was predicted by Einstein. These waves are like the music of a cosmic waltz. But there's a quirk to this waltz: turning right was forbidden. All movements went only to the left.

A group of scientists led by Ilaria Caporali modeled how future detectors — the Einstein Telescope and Cosmic Explorer — could capture this dance. These instruments are interferometers (devices that measure shifts with a laser beam) with arms 15 and 40 kilometers long. They pick up the stochastic background — a mixture of waves from all directions. It turned out that at frequencies above 50 hertz (a low hum, like bass), the waves exhibit circular polarization — they are twisted predominantly in one direction. This parity violation is direct evidence of asymmetry in the early universe.

The same asymmetry could have created an excess of matter over antimatter — without it, stars and planets would never have formed. And dense clumps of matter could have collapsed into primordial black holes. Perhaps they make up dark matter — the invisible mass that holds galaxies together. Scientists used computer modeling and Bayesian inference (a way to estimate probabilities) to show that future detectors will measure this asymmetry with good accuracy.

Thus, after 13,8 billion years, detectors will finally record the forbidden turn of the cosmic waltz. And this music will explain the first steps of the cosmos.