File: 11 October 2026 · Source date: 11 October 2026
What can B-mode carry?
Certain vortex-like patterns in the polarization of the cosmic microwave background may be traces of gravitational waves produced in the early universe. Such a determination would strongly test some inflation models.
Foreground problem
Dust grains aligned with magnetic fields in the Milky Way also produce polarized light. In addition, the gravitational lensing of large-scale structures converts E-modes into B-modes. Multi-frequency sky maps are required to separate these components.
What's the result today?
Joint analysis of BICEP/Keck, WMAP, and Planck data yielded a strong upper bound for the tensor-scalar ratio; it did not report a robust primordial B-mode detection. The absence of the signal does not refute all forms of inflation, but it narrows the field of high-amplitude models.
Related reading
What does the Big Bang explain? · Models ON the end OF the universe
discussion question
Are upper limits or direct determinations more decisive to support a cosmology model?
Resources and further reading
BICEP/Keck XIII — Improved Constraints on Primordial Gravitational Waves ↗ESA Planck — Gravitational waves remain elusive ↗Share your answer
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