Patterns in the Cosmos Trace Evolution of the Universe

Detection of subtle polarization patterns in the Cosmic Microwave Background opens a new window on fundamental physics and cosmology.

Image courtesy of Stephen Hoover (SPT Team member)

The Science

Scientists from the South Pole Telescope project have detected subtle distortions in the universe’s oldest light, the Cosmic Microwave Background (CMB). These distortions—detected for the first time—are observed as twisting patterns in the polarization of the CMB light caused by gravitational lensing and provide a unique probe of the evolution of the universe.

The Impact

These twisting patterns—known as B-modes—arise due to gravitational lensing and may help reveal secrets about the elusive neutrinos through their impact on the growth of structure through the history of the universe, from the time when the CMB light was created (approximately 400,000 years after the Big Bang) up until today. Observation of these difficult to see twisting patterns represents a major achievement and a big step in providing a pathway to tease out information about the earliest moments of the universe, before even the creation of the CMB light itself.

Summary

The CMB microwave radiation we see provides a direct view of the universe when it was approximately 400,000 years old. Prior to then, the universe was a hot soup of electrons, nuclei, and photons known as plasma. As the universe expanded and the plasma cooled, the electrons and nuclei were able to combine to make stable neutral atoms. When that happened, the plasma became less opaque, allowing photons to scatter off of the neutral atoms and eventually stream out of the plasma; this escaping light is what we today call the cosmic microwave background. When this light last scattered it became slightly polarized, like light reflected from the surface of a lake. This polarization, first detected in 2002, does not lead to twisting, or swirl-like, patterns in the sky. However, over the 14 billion years the light has travelled through the evolving universe to reach us, the rays of the light are bent through interactions with massive, large scale structure in the universe, such as those reflected in the distribution of galaxies (The bending of the CMB light is known as gravitational lensing.) By making highly sensitive measurements of the polarization of the CMB at arc minute resolution (about the angular resolution of the human eye) the researchers were able to detect the tell-tale right- and left-handed polarized swirl patterns, which physicists call “B-modes.” They are very difficult to tease out of the data, as their strength are only a small fraction of the unperturbed polarization signal, which itself it much weaker than the unpolarized signal. It represents a major achievement of the South Pole Telescope collaboration that it has been able to observe these B-modes.

A study of these swirls should add to our growing knowledge of the history of the universe and the role played by dark matter and dark energy. The B-mode measurements will also help put limits on neutrino masses, those strange but incredibly abundant particles that flood the universe. But physicists are even more excited by an additional prospect. If B-mode polarization patterns can be detected on much larger angular scales, and with much higher sensitivity, they would have something to say about the inflationary period of our very early universe long before the CMB was created. Theorists believe the inflationary period occurred within the first instants of the Big Bang and led to an expansion rate faster than the speed of light. If such is the case, then gravitational waves from the inflationary period may have left their signature/imprint on the CMB through B-mode polarization as well. Many believe that this would provide the definitive experimental confirmation of the inflationary universe.

Contact

John Carlstrom
Argonne National Lab
jc@kicp.uchicago.edu

Funding

The SPT is supported by the National Science Foundation through grant ANT-0638937, with partial support provided by NSF grant PHY-1125897. Support at Argonne National Laboratory for the development of SPTpol and data analysis is supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC02-06CH11357. Further support of the development and construction of the SPTpol receiver were provided by the Kavli Foundation, the Gordon and Betty Moore Foundation through Grant GBMF 947 to the University of Chicago, and NSF award 0959620.

Publications

D. Hanson et al., “Detection of B-mode Polarization in the Cosmic Microwave Background with Data from the South Pole Telescope.” arXiv:1307.5830 [astro-ph.CO] (http://arxiv.org/abs/1307.5830)