page_title: Physical cosmology
section_title: Cosmic microwave background
hierarchical_section_title: Physical cosmology / Areas of study / Cosmic microwave background
caption_attribution_description: English: Superconducting Detectors for Study of Infant Universe http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA17993 http://www.jpl.nasa.gov/news/news.php?release=2014-082 The BICEP2 telescope at the South Pole uses novel technology developed at NASA's Jet Propulsion Laboratory in Pasadena, Calif. The focal plane shown here is an array of devices that use superconductivity to gather, filter, detect, and amplify polarized light from the cosmic microwave background -- relic radiation left over from the Big Bang that created our universe. The microscope is showing a close-up view of one of the 512 pixels on the focal plane, displayed on the screen in the background. Each pixel is made from a printed antenna that collects polarized millimeter-wavelength radiation, with a filter that selects the wavelengths to be detected. A sensitive detector is fabricated on a thin membrane created through a process called micro-machining. The antennas and filters on the focal plane are made from superconducting materials. An antenna is seen on the close-up shot in the background with the green meandering lines. The detector uses a superconducting film as a sensitive thermometer to detect the heat from millimeter-wave radiation that was collected by the antenna and dissipated at the detector. A detector is seen on the close-up shot in the background to the right of the pink square. Finally, a tiny electrical current from the sensor is measured with amplifiers on the focal plane called SQUIDs (Superconducting QUantum Interference Devices), developed at National Institute of Standards and Technology, Boulder, Colo. The amplifiers are the rectangular chips on the round focal plane. The focal planes are manufactured using optical lithography techniques, similar to those used in the industrial production of integrated circuits for computers.
context_page_description: Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood. Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang theory, by Georges Lemaître, as the leading cosmological model.
context_section_description: The cosmic microwave background is radiation left over from decoupling after the epoch of recombination when neutral atoms first formed. At this point, radiation produced in the Big Bang stopped Thomson scattering from charged ions. The radiation, first observed in 1965 by Arno Penzias and Robert Woodrow Wilson, has a perfect thermal black-body spectrum. It has a temperature of 2.7 kelvins today and is isotropic to one part in 10⁵. Cosmological perturbation theory, which describes the evolution of slight inhomogeneities in the early universe, has allowed cosmologists to precisely calculate the angular power spectrum of the radiation, and it has been measured by the recent satellite experiments (COBE and WMAP) and many ground and balloon-based experiments (such as Degree Angular Scale Interferometer, Cosmic Background Imager, and Boomerang). One of the goals of these efforts is to measure the basic parameters of the Lambda-CDM model with increasing accuracy, as well as to test the predictions of the Big Bang model and look for new physics. The results of measurements made by WMAP, for example, have placed limits on the neutrino masses.
  Newer experiments, such as QUIET and the Atacama Cosmology Telescope, are trying to measure the polarization of the cosmic microwave background. These measurements are expected to provide further confirmation of the theory as well as information about cosmic inflation, and the so-called secondary anisotropies, such as the Sunyaev-Zel'dovich effect and Sachs-Wolfe effect, which are caused by interaction between galaxies and clusters with the cosmic microwave background.
  On 17 March 2014, astronomers of the BICEP2 Collaboration announced the apparent detection of B-mode polarization of the CMB, considered to be evidence of primordial gravitational waves that are predicted by the theory of inflation to occur during the earliest phase of the Big Bang. However, later that year the Planck collaboration provided a more accurate measurement of cosmic dust, concluding that the B-mode signal from dust is the same strength as that reported from BICEP2. On 30 January 2015, a joint analysis of BICEP2 and Planck data was published and the European Space Agency announced that the signal can be entirely attributed to interstellar dust in the Milky Way.
caption: Evidence of gravitational waves in the infant universe may have been uncovered by the microscopic examination of the focal plane of the BICEP2 radio telescope.[9][10][11][41]
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