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We are interested in answering some of the biggest and most exciting questions about the nature of the Universe. What was the Universe like at the beginning of time? How did the Universe come to be the way it is today? Through precision measurements of the Cosmic Microwave Background (CMB), we directly explore the Universe as it was shortly after the Big Bang, and hope to solve some of the mysteries that exist in Cosmology today.

What is the CMB?

After the Big Bang, the Universe was a hot, dense plasma which began to expand and cool. When the temperature cooled enough (380,000 years after the big bang), electrons could combine with protons to form hydrogen atoms. The photons which comprise the Cosmic Microwave Background (CMB) were emitted as a biproduct of this process, and these same photons are still traveling through the Universe today. Because the CMB is the oldest light in the Universe, it is an extremely powerful tool that we can use to probe the nature of the Universe at very early times. Precision measurements of the CMB in the last few decades, have shown remarkable agreement with the Standard Model of Cosmology, corroborating the hot Big Bang model. Recent measurements of the CMB have revealed a few features that are surprising in the context of a hot Big Bang model. The entire observable Universe was suprisingly homogeneous (to one part in 100,000) at the time of last scattering, but we expected that only portions of the Universe that were in causal contact with each other (ie. closer than the size of the horizon) would be homogeneous. Moreover, the geometry of space was found to be extremely flat, a suprising result given that the Universe can only be flatter in the early Universe than it is today.

The CMB and Inflation

Inflation is a theory which provides a neat solution to these "problems." According to the theory of Inflation, the Universe underwent a violent and rapid expansion at only 10^-35 seconds after the Big Bang, making the horizon size much larger, and allowing the space to become flat. Confirmation of Inflation would be an amazing feat in observational Cosmology. Inflation during the first moments of time produced a Cosmic Gravitational-Wave Background (CGB), which in turn imprinted a faint but unique signature in the polarization of the CMB. Since gravitational waves are by nature tensor fluctuations, the polarization signature that the CGB stamps onto the CMB has a curl component (called "B-mode" polarization). In contrast, scalar density fluctuations at the surface of last scattering only contribute a curl-free (or "E-mode") polarization component to the CMB which was first detected by the DASI experiment at the South Pole.

BICEP1, BICEP2, Keck Array, and BICEP3

Observing from the South Pole, this series of experiments aims to discover signatures of Inflation by actually detecting the CGB via its weak imprint as the unique B-mode polarization signature of the CMB, directly probing the Universe at an earlier time than ever before. Each generation represents a large increase in sensitivity to B-mode polarization. BICEP1 observed from 2006-2008 with 98 detectors, BICEP2 began observing in the beginning of 2010 with 512 detectors, and the first three of five Keck Array telescopes began observing in the beginning of 2011, each with 512 detectors. The final two Keck Array receivers were deployed during the summer season of 2012. BICEP3, with a total of 2,560 detectors, will begin observing in 2015.

This material is based upon work supported by the National Science Foundation.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s)
and do not necessarily reflect the views of the National Science Foundation.
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