Is the universe twisted? A new check on a possible twist in the universe's oldest light
The cosmic microwave background (CMB) is the universe's oldest light, leftover thermal radiation from about 380,000 years after the big bang. Maps of the CMB offer a picture of the "baby universe" as it was 13.8 billion years ago.
This study, published in The Astrophysical Journal Letters, examines the possibility of a twist in the universe's oldest light, known as the cosmic microwave background (CMB). The CMB is the remnant thermal radiation from approximately 380,000 years following the big bang. The polarization of this light could potentially reveal information about the universe's fundamental nature, including physics beyond the Standard Model and clues about dark matter and dark energy.
Scientists have observed hints that this polarization might have rotated slightly as it traveled through the cosmos. If verified, this phenomenon, known as cosmic birefringence, could offer evidence supporting new physics theories and help clarify the properties of dark matter and dark energy.
However, accurately measuring this rotation is challenging due to the potential for instrumental errors to produce similar effects. Researchers from the University of California, San Diego, have developed a method to test the relative polarization-angle calibration of different detector sets. This technique compares maps generated from various detector groups and can identify calibration discrepancies that could mimic a cosmic rotation.
The team applied their method to eight Planck polarization maps and compared the resulting calibration pattern with the established Minami–Komatsu analysis. The two approaches were consistent, suggesting the new method can reliably distinguish between calibration errors and genuine cosmic rotation.
The researchers anchored their calibration comparison to an existing analysis, which produced a cosmic-birefringence angle of 0.37 ± 0.12 degrees. This result aligns with previous findings but still depends on an independent absolute calibration reference. The development of this calibration technique could enhance the search for primordial B-modes, which would provide significant evidence about gravitational waves in the early universe and support specific models of cosmic inflation.
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