Cosmic Background Radiations
 
Overview
Cosmic background radiations thread the tapestry of cosmological physics. Studying them provides a wealth of information on everything from inflation during the earliest epochs of the universe to the formation of cosmological structures during more recent epochs. Fifty years ago, the field of cosmology was largely a collection of untestable postulates. But today, thanks largely to research into the cosmic microwave background radiation (CMB), cosmology is a precise, quantitative science with important consequences that range from classical astronomy to high-energy physics. A key goal of modern observational cosmology is to understand and trace the formation of large-scale structure throughout the history the Universe. We now know from CMB studies that when the universe was about 300,000 years old, its matter distribution was extremely uniform. As time progressed gravitational collapse amplified the small deviations from uniformity into the rich structures that we see in the Universe today. Many experiments have measured tiny differences in the brightness or temperature of CMB at different points on the sky. This has yielded important insights into how the early universe was put together. Researchers at the Kavli Institute for Cosmological Physics are conducting experiments to measure and understand two key types of cosmic background radiations - the Cosmic Microwave Background radiation (CMB) and the Cosmic Infrared Background radiation (CIB).
 
What is the Cosmic Microwave Background radiation (CMB)?
The Cosmic Microwave Background Radiation (CMBR) is light reaching Earth that was produced 300,000 years after the Big Bang when the universe was only 1/1000 of its current size. This radiation was produced at a specific epoch in the history of the Universe - when the matter had cooled enough that light could stream freely though the Universe without being scattered by electrons. Since this radiation was emitted at a specific time in the history of the expansion of the Universe it carries with it the signatures of the structure of the Universe at that epoch. Detailed measurements of this radiation therefore describe the structure and composition of the early Universe.
 
Which KICP experiments inform our understanding of the CMB?
In 2002 the DASI experiment (lead by KICP faculty member John Carlstrom) made the first detection of the polarization of the CMB anisotropy (a component known as the E-mode), which had been predicted by standard models of the early universe. This was subsequently confirmed by the WMAP satellite. Several experimental efforts in our Institute are working toward improving the experimental limits on the measurement of the polarization of the CMB to discern the fine-scale structure of this polarization and working towards detecting a much lower level of polarization expected from gravitational waves (a component known as the B-mode). The experiments that are focused on this effort are the CAPMAP experiment that is currently underway (in 2004) and two future experiments, which are in the design and planning phases - QUIET and the Kavli Polarimeter on the South Pole Telescope. This suite of experiments should provide important, independent information about early-universe physics.
 
What is the Cosmic Infrared Background Radiation (CIB)?
When the Universe was between 300,000 and 6 billion years old, the gas which had gravitationally collapsed enough to form the first "galaxies" were sufficiently compressed to ignite - or form the first population of stars. These stars are believed to have been encased on dust which obscured the light from them. The light from this first generation of stars is believed to have heated up the only enough for the dust to be heated up and to re-emit it in the infrared. The radiation we receive from this population of protogalxies is further redshifted as it travels to us and is observable by telescopes at sub-mm wavelengths. The Cosmic Infrared Background Radiation (CIB) is the integrated light from all such dust in the line-of-sight and not from protogalaxies at a specific redshift (unlike the CMB radiation). Consequently, the CIBR traces how these galaxies are distributed through space.
 
What will the EDGE experiment do to improve our understanding of the CIB?
The EDGE experiment is a balloon-borne experiment that will study variations in the CIB anisotropy produced by young galaxies. This can explore how large-scale cosmological structures evolve, and test the standard cold dark matter paradigm of galaxy formation.

EDGE will measure the "clumpiness" of the CIB across the sky, back to the time the first galaxies ignited. This will help fill in the gap that exists between the measurements from the CMB, and those from the modern era. The end result should be more complete history of large-scale structure formation.