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Photons’ journeys across the universe help unravel cosmological mysteries

Posted February 17, 2014
Photons’ journeys across the universe help unravel cosmological mysteries
Polarization maps illustrating the rotation of photon polarization. Credit: Liang Dai. ©2014 American Physical Society
The faint background glow that exists throughout the Universe, called the Cosmic Microwave Background (CMB), is made of photons that have been scattering since the universe was just 400,000 years old. Now in a new paper, physicist Liang Dai at Johns Hopkins University in Baltimore, Maryland, has shown that the polarization of these photons is rotated as they travel by things such as gravity waves and cosmic matter flows. By accounting for this rotation effect when observing the CMB photons, scientists may be able to investigate parts of the Universe that might otherwise remain unknown.

“The CMB is like a cosmic back light,” Dai told “When the CMB photons finally reach us today, they have traversed vast cosmic space, and are distorted by whatever lies in between. It is of great significance to study/measure these distortions (to both temperature and polarization) because we then learn about the distribution and evolution of the ‘stuff’ in between, and hence understand the more recent Universe.”

This ‘stuff’ that distorts the CMB photons on their journey includes the large-scale structure of matter in the Universe, as well as less visible stuff, such as primordial gravity waves and vortical cosmic matter flows (for example, the circular collective movement of galaxies).

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