CMB / POLARBEAR

What is CMB?

The Cosmic Microwave Background (CMB) is the oldest light that we can observe today. It was created when the Universe was only 380,000 years old and filled the entire Universe. At that time, the Universe had expanded enough to become less opaque and allowed photons to escape from interacting with free particles. More than 13 billion years after that, the Universe has been continually expanding and cooling. The wavelength of these photons has been shifted (also known as “redshifted”) and their temperature has decreased to just 2.7 Kelvin as we observe today.

Because the CMB is the furthest backlight we can study, it is the most important evidence for understanding the origin of the Universe. Furthermore, as they traveled across the Universe, CMB photons were deflected by the gravitational lensing effect from cosmic structures (the large-scale structure). This deflection helps us understand the composition and formation of structure in the Universe.

What is POLARBEAR?

POLARBEAR is a CMB polarization experiment located in northern Chile. Our primary goal is to detect a faint CMB B-mode signal — evidence of inflationary theories — which predict the early universe underwent a phase of rapid expansion generating primordial gravitational waves. These gravitational waves imprinted their signature, a primordial B-mode polarization, into the CMB.

Additionally, gravity from early times influenced the universe to form large-scale structures observable today. These structures distorted early CMB photons and transformed E-mode to B-mode polarization. POLARBEAR measurements also help us understand the neutrino mass and dark energy.

POLARBEAR was deployed in the Atacama Desert in October 2011 and saw first light in January 2012. Since then the collaboration has published numerous results, including the first detection of CMB B-mode polarization from gravitational lensing in 2014.

What is the Simons Array?

The Simons Array is the expansion of POLARBEAR. When completed, it will consist of three telescopes, each with more than 7,500 dual-polarization detectors — over 22,000 total, 18 times more than POLARBEAR. Combined with more advanced readout technology, this greatly enhances our capacity to detect the inflationary B-mode signal.

Why Chile?

Atmospheric water vapor absorbs and attenuates millimeter-wave photons, obstructing CMB observations. At over 5,000 meters above sea level, the Atacama Desert is one of the driest places on Earth — making it ideal for CMB telescopes, including POLARBEAR.

Want to know more?

Key publications from the POLARBEAR/Simons Array collaboration:

1. Z. Kermish et al. “The POLARBEAR Experiment,” Proc. SPIE 8452, 84521C (2012). doi:10.1117/12.926354
2. The POLARBEAR Collaboration. “A Measurement of the CMB B-mode Polarization Power Spectrum at Sub-degree Scales with POLARBEAR,” ApJ, 794, 171 (2014). doi:10.1088/0004-637X/794/2/171
3. The POLARBEAR Collaboration. “Measurement of the CMB Polarization Lensing Power Spectrum with POLARBEAR,” PRL, 113, 021301 (2014). doi:10.1103/PhysRevLett.113.021301
4. N. Stebor et al. “The Simons Array CMB Polarization Experiment,” Proc. SPIE 9914, 99141H (2016). doi:10.1117/12.2233103
5. P. Siritanasak et al. “Broadband AR-Coated Extended Hemispherical Silicon Lenses for POLARBEAR-2,” JLTP, 184, 553 (2016). doi:10.1007/s10909-015-1396-x
6. The POLARBEAR Collaboration. “A Measurement of the CMB B-mode Power Spectrum from Two Years of POLARBEAR Data,” ApJ, 848, 121 (2017). doi:10.3847/1538-4357/aa8e9f
7. The POLARBEAR Collaboration. “A Measurement of the Degree-Scale CMB B-Mode Angular Power Spectrum with POLARBEAR,” ApJ, 897, 55 (2020). doi:10.3847/1538-4357/ab8f24

For the full list of publications, see the publications page.

"The Universe is under no obligation to make sense to you."