Cosmic Microwave Background (CMB)

The Cosmic Microwave Background (CMB) is the oldest detectable light in the universe, and is an invaluable tool for learning about the early universe, the evolution of the universe, and the fundamental physics that govern the universe on its smallest and largest scales. Microwave telescopes at the South Pole and in Chile observe the CMB, which is a bath of microwave radiation that was emitted a mere 380,000 years after the Big Bang, when the universe underwent a phase transition to neutral hydrogen. Measurements of its spacial fluctuations in temperature and polarization have revealed information about the contents and evolution of the universe. Current and future telescopes focus on making precision measurements of the polarization of the CMB, to measure the mass of the neutrino through observations of the large scale structure of the universe, and to probe the nature of a potential inflationary epoch in the first tiny fraction of a second after the Big Bang by measuring the imprint of primordial gravitational waves on the polarization of the CMB. The next generation of ground-based CMB telescopes, such as CMB-S4, will attain the best precision with full sky coverage, which is especially important for the goal of measuring properties of neutrinos. Currently both actively-used CMB sites are in the Southern hemisphere, and Summit Station is an attractive Northern site because of its high altitude and dry, stable atmosphere. The team is currently performing site characterization at Summit Station to determine how a CMB telescope would perform at the site compared to South Pole and Chile. In 2016, they deployed a 183 GHz Water Vapor Radiometer with scanning optics that perform 360 degree scans continuously in azimuth and periodic full sky dips in elevation. They are measuring the fluctuations in atmospheric millimeter-wave power on timescales and angular scales relevant for CMB observations to determine the potential noise contribution to CMB maps. An identical unit is deployed at the South Pole for comparison.