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Early Universe Symmetry Violations Could Explain Why Matter Exceeds Anti-Matter Today

If the findings are confirmed, this will represent a step towards explaining one of physics’ most troubling problems.


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

The distribution of galaxies, such as these known as Abell 2744 reveals an asymmettry dating back to the first moments of the universe.

The distribution of galaxies, such as these known as Abell 2744, reveals an asymmettry dating back to the first moments of the universe.

Image Credit: NASA/ESA

The symmetry in the laws of physics that holds matter and anti-matter to be perfect reflections of each other didn’t apply shortly after the Big Bang, new evidence suggests. The work could offer an explanation for the troubling fact that, although the universe operates on symmetric laws, antiparticles are far from equally abundant.

A universe that contained equal amounts of matter and anti-matter would be one in which the two were constantly eliminating each other in bursts of energy. Not a likely place for life to evolve, let alone make the long journey to beings capable of grasping the laws of physics. Yet those laws, as we currently understand them, suggest equal amounts of each substance should have been created with the universe.


Somehow we escaped this fate, with matter vastly predominating. This observable fact means that, somewhere along the line, the universe was not perfectly symmetric. Cosmologists have spent almost 60 years seeking the point where symmetry failed. A new paper in the Monthly Notices of the Royal Astronomical Society (MNRAS) claims to narrow it down to the so-called “inflationary era”.

Dr Robert Cahn, Professor Zachary Slepian, and Dr Jiamin Hou proposed that the secret to finding where symmetry broke down might lie in the distribution of galaxies. Their reasoning has been published in Physical Review Letters, but the more exciting news is that in the MNRAS paper, they claim to have found anomalies in galactic distribution they can’t explain any other way.

“A tetrahedron [triangular pyramid] is the simplest shape that cannot be rotated into its mirror image in three-dimension (3D),” the authors note in MNRAS. Any four galaxies (a quadruplet) can be made to form a tetrahedron’s points. In an entirely symmetric universe, we would expect to see equal numbers of one orientation of a tetrahedron and its mirror image. If we see more examples of one than the other, it indicates a failure of symmetry at the point when the lumpiness of the universe’s mass arose.

Studying more than a million bright red galaxies identified in two surveys the authors did indeed find an unequal distribution that implies a lack of symmetry was present at this time. Exactly what that asymmetry was, and where it has gone over the subsequent 14 billion years, remain unanswered questions. Nevertheless, if the work is replicated, we’d be able to narrow our search.


"I've always been interested in big questions about the universe. What is the beginning of the universe? What are the rules under which it evolves? Why is there something rather than nothing?" said Slepian in a statement. "This work addresses those big questions."

Big questions are seldom answered easily, and analyzing such immense samples of galaxies was an extraordinarily involved task. It wasn’t simply a matter of finding neatly clustered sets of four galaxies and categorizing each as either a left or right-handed tetrahedron. Instead, the team needed to have a supercomputer draw lines between each galaxy and three others to produce a tetrahedron, then do the same thing again with another three, and so on. Lines hundreds of millions of light years long were drawn to connect immensely distant galaxies into tetrahedrons far larger than even the largest galactic cluster.

“Eventually we realized we needed new math,” Slepian said. The formulae meant it didn’t take the computer a substantial portion of the age of the universe to crunch through the possible combinations. It was even able to rerun the calculations repeatedly to check they are right.

The imbalance the team found in one sample of galaxies was highly unlikely to be by chance, and the other was even less plausible. Now, however, they plan to do the same thing all over again with larger galactic samples being produced by a generation of more advanced telescopes.


The one existing violation of symmetry known is in the weak force, but as the papers note, its range is too short to account for deviations on a galactic scale, so the cause has to be something else.

Among other things, the work provides the potential to settle the debate between the inflationary and non-inflationary models of the universe’s early expansion. "Since parity violation can only be imprinted on the universe during inflation, if what we found is true, it provides smoking-gun evidence for inflation," Slepian said.

The evidence for asymmetry is published in Monthly Notices of the Royal Astronomical Society

The basis for the search was submitted in 2021 to Physical Review Letters, but has only just been published.


spaceSpace and PhysicsspaceAstronomy
  • tag
  • cosmic inflation,

  • antimatter,

  • Astronomy,

  • Symmetry violations,

  • distribution of galaxies,

  • galactic quodruplet,

  • tetrahedron