The early Universe was not just a hot soup of particles. In the first fractions of a second, mirror symmetry could have been broken: the world and its reflection would not be quite identical. If so, the large-scale cosmic web of galaxies would retain a barely noticeable 'curl'—as if all matter were slightly twisted in one direction.
The research team figured out how to measure this twist. They built an estimator based on helicity — a quantity that shows how much a structure of dark matter resembles a right-handed or left-handed corkscrew. Computer simulations with artificially imposed asymmetry confirmed that even after billions of years of evolution, the trace does not fade. Then they applied the method to real data — the galaxy map from the Sloan Digital Sky Survey (SDSS).
The result was borderline: there is a slight hint of 'left-handedness', but it is too weak to claim a discovery. The statistical significance is insufficient. However, the main achievement is different — astronomers now have a working tool to search for the imprint of the early Universe in the distribution of galaxies. Future surveys, such as Euclid or Roman, will provide maps hundreds of times more detailed, and then the question of the mirror symmetry of the cosmos may finally be resolved.
The weak interaction is the only one of the four fundamental forces for which parity violation has been definitively proven. Electrons in beta decay predominantly come out 'left-handed', and this discovery in 1956 came as a shock to physicists.
In Peter Watts's novel Blindsight, an alien intelligence uses parity violation in its biochemistry, making it invisible to human perception.