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A Chicago Perspective on an Exciting Cosmological Discovery

The BICEP2 telescope in the foreground, with the South Pole Telescope in the background. The Sun is setting for the 6 months of darkness during the South Pole winter.

The BICEP2 telescope in the foreground, with the South Pole Telescope in the background. The Sun is setting for the 6 months of darkness during the South Pole winter.

On Monday March 17, 2014 a major step in our understanding of the earliest phases of the Universe was announced, with the detection by the BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) Collaboration of the imprint of gravitational waves on matter and space. Since the mid-1990s, it was theorized that a detection of B-mode polarization in the Cosmic Microwave Background (CMB) would provide an important constraint on inflationary models, which describe the rapid expansion of the Universe in the first 10^−32 seconds (a tiny fraction of a second) since the Big Bang. As inflationary models developed, predictions for a small expected level of B-mode polarization were put forth, so the relatively high amount detected by BICEP2 is an exciting result. For more background on polarization in the CMB, and the science leading up to the BICEP2 detection, see the recent Adler blog from February 2014.

The BICEP2 image of a 15 degree by 60 degree part of the Southern sky, showing the detected B-mode polarization signal.

The BICEP2 image of a 15 degree by 60 degree part of the Southern sky, showing the detected B-mode polarization signal.

Following the announcement on Monday, the University of Chicago held a BICEP2 extravaganza on Wednesday, March 19 in which lead researchers from the BICEP2 Collaboration, Dr. Chris Sheehy and Dr. Abigail Vieregg from the University of Chicago, and Dr. Clem Pryke from the University of Minnesota, presented their results. In particular, they detailed the painstaking study of systematic uncertainties in the analysis, such as unknown noise in the images of the sky, and for any possible contamination in the B-mode polarization signal (i.e. from cosmic dust). Dr. Sheehy writes: "We all put in long hours of work for this. As one of the people responsible for investigating possible instrumental systematics, I definitely felt a responsibility to be thorough. It's easy to work long hours when the thought of possible mistakes is already keeping you up at night!"

Commenting on the sense of discovery with the detection, Dr. Sheehy writes: "Certainly the signal we saw was bigger than we expected, but we explicitly decided to keep an open mind. We knew we were making measurements that had never been made, and predictions about what would be possible to see were just that - predictions, not guarantees."

University of Chicago scientist Dr. Brad Benson provides perspective on this result, working with the complementary South Pole Telescope (SPT). Dr. Benson writes: "The BICEP2 results are extremely impressive, and I’m very confident that they are correct.  However, with any discovery this significant, it will be important to verify it with another experiment, and I think the scientific community will want to see that.  There are a handful of experiments with the ability to confirm the BICEP2 measurements, and I feel confident that one of them can do it in the next couple years. The potential to do this with SPTpol (a camera located on the South Pole Telescope) is very exciting, and this now becomes the highest priority science goal for SPTpol. Congrats to the entire BICEP2 team! It is a very exciting result for the entire astrophysics community!"

You can explore the South Pole Telescope in our exhibition, Telescopes: Through the Looking Glass. Questions for BICEP2 and the SPT? You can tweet them @BICEPTWO and @SPTelescope. As always you can ask the Adler your questions on Facebook or Twitter

Written by Dr. Jeff Grube, postdoctoral researcher at the Adler Planetarium.

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