New Test Supports Cosmic Birefringence in Ancient Light

Researchers propose a method to separate true cosmic birefringence from observational bias in CMB polarization data. Comparing eight Planck polarization maps, they found the small polarization shift first reported in 2020 appears cosmic in origin, challenging the standard cosmological model.

• Method compares observation sets: true birefringence is identical across sets, bias varies
• Eight Planck cosmic microwave background polarization maps were analyzed
• The polarization shift was first reported in 2020 and should be zero under the standard model
• Result is not conclusive; more observations are needed to confirm it