Roughly 400,000 years after the Big Bang, the universe cooled enough for photons to escape from the primordial cosmological soup. These ancient photons, known as the Cosmic Microwave Background (CMB), have traveled over 14 billion years.
In a recent study, scientists utilized data collected from the South Pole Telescope at the National Science Foundation's Amundsen-Scott South Pole Station in Antarctica to examine the theoretical framework of the standard cosmological model. This research was conducted by UC Davis researchers and collaborators within the South Pole Telescope collaboration led by the University of Chicago and has been submitted to Physical Review D.
The study supports the standard cosmological model through high-precision measurements of CMB and its polarized light. It introduces a new method for calculating the Hubble constant, providing insights into "the Hubble tension," an ongoing scientific debate regarding how fast the universe is expanding.
Lloyd Knox, co-author and Michael and Ester Vaida Endowed Chair in Cosmology and Astrophysics at UC Davis, remarked, “We have a largely coherent, detailed, and successful model describing these 14 billion years of evolution.” He added that there remains uncertainty about what generated initial deviations from homogeneity leading to all structures in the universe.
Tom Crawford from University of Chicago noted, “This result is especially exciting because it represents the first competitive constraints on cosmology using only the polarization of CMB.”
Researchers analyzed two years of polarized light data from 2019 and 2020 covering 1,500 square degrees of sky. The data helped create a large-scale map of mass in the universe. Most natural light is unpolarized; however, when reflected it can become polarized—a phenomenon observed with cosmic microwave background photons during their final scattering events.
Knox explained that their measurements captured both polarization degree and orientation across their sky map. Gravitational lensing distorts paths of these light rays creating warped images which were analyzed using computers at Berkeley's National Energy Research Scientific Computing Center (NERSC).
Marius Millea described their process: “What we essentially do at a really high level is we have this data and we send it over to this supercomputer at NERSC.” Fei Ge added that having both data and predictive models was crucial.
The research addresses "the Hubble tension," where different methodologies yield varying expansion rates for our universe. Their prediction aligns with those made using Planck satellite measurements but shows discrepancies with supernovae observations—a major puzzle in contemporary cosmology.
Their findings add another layer any resolution to "the Hubble tension" must consider: predictions consistent with standard models yet precise enough against supernovae measures.
Citation: “Cosmology From CMB Lensing and Delensed EE Power Spectra Using 2019-2020 SPT-3G Polarization Data.” Ge et al., submitted to Physical Review D.
Funding for this work comes from NSF’s Office of Polar Programs & U.S Department Of Energy’s Office Of Science High Energy Physics.