Old Universe, New Twist

Anto Lonappan and Brian Keating, made with AI assistance Visualization of the rotation of E-modes to B-modes by cosmic birefringence. We are bathed in light from the ancient cosmos. It began its journey when the Universe finally cooled enough to be transparent, and it has traveled for more than 13 billion years to reach us. We call it the cosmic microwave background (CMB), and it has much to tell us. One of the more subtle bits encoded in the cosmic background is polarization. When the Universe became optically transparent around 380,000 years after the Big Bang, those old photons had one last scatter off a hydrogen atom before undertaking their great journey. This “last scattering” polarized the photon. Initially the CMB photons were polarized randomly and had no large-scale orientation. But much can happen over 13 billion years. Baumann, et al (2009) E-mode and B-mode polarizations. There are two basic ways that cosmological photons can shift at observable scales. The first is…