A subtle twist in the universe’s oldest light may be bigger than we thought

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doi.org/10.1103/6z1m-r1j5
Credibility: 989
#CMB

Cosmic microwave background radiation, known as CMB, is the oldest light we can observe: a faint echo of the Big Bang, which traveled through space for almost 14 billion years to reach us

This light carries precious information about the primordial universe, and part of it is polarized – that is, its waves vibrate in specific directions, as if they were aligned arrows.

Scientists have discovered that this polarization can undergo a small rotation during the long journey through the cosmos, an effect called cosmic birefringence.

It is as if the ancient light has been subtly “twisted” along the way.

Previous studies estimated this twist at about 0.3 degrees – a very small but intriguing value, because the standard model of physics does not predict such a rotation.

Now, a team led by Fumihiro Naokawa, a doctoral candidate at the University of Tokyo, in collaboration with Toshiya Namikawa of the Kavli Institute for the Physics and Mathematics of the Universe, has developed a new way to analyze these measurements.

They looked more carefully at the uncertainties involved and discovered something important: there is a 180-degree ambiguity in measuring the rotation angle.

Imagine a clock: just looking at the hands, you don’t know if it’s noon or midnight plus 12 hours – the hand could have turned an extra half turn without you noticing.

Likewise, the CMB light we see today may have rotated 0.3 degrees…

or 180.3 degrees…

or even more full turns.

By studying the detailed shape of the signal (especially the correlation between the E and B modes of polarization), the researchers were able to reduce this ambiguity.

The result suggests that the actual twist may be greater than the 0.3 degrees previously reported.

This correction not only improves accuracy but also shows that cosmic birefringence influences other important measurements, such as the optical depth of the universe (related to the time when the first stars and galaxies “reionized” the cosmos), which may require adjustments to our cosmological models.

Why does this matter so much? If confirmed, a greater rotation would indicate a break in left-right symmetry in the universe – something that the standard model does not explain and that could point to new physics.

Possible culprits include hypothetical particles like axions, which could solve dark matter mysteries, or even effects linked to dark energy.

It would be a sign that the universe has a subtle preference for one side rather than being perfectly symmetrical.

The discovery still needs further confirmation, especially with data from future telescopes like the Simons Observatory and LiteBIRD.

But it already represents an important advance: by resolving this phase ambiguity, scientists are refining our view of the oldest light in the universe and opening doors to better understand what happened in the earliest moments of the cosmos – and perhaps discover secrets we have not yet imagined.

Published in 03/13/2026 07h24

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Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.

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