Embedded Files
Published: 23rd October, 2025, Academia Sinica, Institute of Astronomy & Astrophysics (ASIAA), Taiwan
Using N-body cosmological simulations, an international team led by Dr. Junsup Shim from the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has shown that the spins of present-day galaxies can reveal whether a fundamental symmetry—parity symmetry—was broken in the early Universe. Their findings suggest that such signatures could be detected with upcoming survey data, offering important clues to the handedness of the cosmos. The results were published in Physical Review Letters and featured as a Synopsis in Physics Magazine in October, 2025.
Is our Universe left-handed or right-handed? It may sound like a strange question, but it touches on one of the most fundamental ideas in physics — parity symmetry, the principle that the laws of nature should behave the same when viewed in a mirror. If this symmetry were broken in the early Universe, it could point to entirely new physics beyond the standard models of cosmology and particle theory.
A recent study led by Junsup Shim and colleagues has taken a major step toward testing this cosmic handedness. Using cosmological N-body simulations, the team developed a novel method to create a Universe with parity-violating initial conditions — in other words, a simulated cosmos born with a preferred handedness. “We discovered that the galaxy rotation map at the present day becomes different when the primordial parity symmetry is broken,” said Shim. This approach enabled the researchers to track how such an asymmetry in the early Universe evolved into the large-scale structures we observe today.
The team found that even after billions of years of cosmic evolution, a substantial fraction of the primordial parity asymmetry survives — encoded in the spins of galaxies. By studying how galaxies rotate, they showed that it is possible to detect traces of this ancient symmetry breaking in real observations. Their analysis predicts that mapping galaxy spins using data from upcoming surveys, such as the Dark Energy Spectroscopic Instrument (DESI), could reveal signs of parity violation with remarkable statistical significance, opening a new window into the physics of the early Universe.
“As galaxies still carry the fingerprints of their asymmetric beginnings,” said Shim, “observing how they spin today may help us uncover the fundamental physical processes that shaped our cosmos.”
Matter distribution in the early Universe simulated with (left) and without (right) parity symmetry, showing the effect of primordial handedness. Image Credit: Junsup Shim
More Information:
This research presented in a paper "Probing Vector Chirality in the Early Universe,” by Shim et al. has appeared in the Physics Review Letters on Spetember 30, 2025. This paper was selected by the PRL editor as a featured Synopsis and appeared in Physics Magazine.
Media Contact:
Dr. Junsup Shim, Email:jshim@asiaa.sinica.edu.tw, Tel: +886 2 2366 5419
Page updated
Report abuse