Cosmic Microwave Background (CMB)


The Cosmic Microwave Background, or CMB, is a faint glow in microwave radiation that is almost perfectly uniform across the sky. This thermal radiation was emitted about 380,000 years after the Big Bang, as the universe became transparent for the first time. 

The CMB peaks at a wavelength of about 2 mm with a nearly perfect blackbody spectrum corresponding to a temperature of 2.73 K. Although the CMB is extremely uniform, there are slight polarizations and variations in temperature throughout. These very faint features offer important glimpses into the physics of the early universe.

Researchers at SLAC participate in the BICEP, BICEP2 and BICEP3 experiments through the group of Chao-Lin Kuo. The group also actively works on the next generation telescope, the Keck Array, which is observing at the South Pole from 2011-2016 (expected). The primary goal of the BICEP experiment/Keck Array is to measure the very faint polarization of the CMB. Cosmologists believe the Universe experienced a rapid period of cosmic inflation during its first fraction of a second, exponentially expanding from a dense, hot subatomic volume. Many models of inflation predict that this rapid acceleration would have generated gravitational waves that would remain energetic enough 380,000 years later to leave an imprint on the CMB. The experiment targeted this imprint by measuring the pure-curl component of the CMB polarization on degree angular scales, which is largely free of contamination from sources other than primordial gravitational waves. The approach taken in the BICEP/BICEP2/Keck Array/BICEP3 family of telescopes is aimed at increasing the sensitivity of the telescope at the degree angular scales by using cold, refractive optics.

Read more about CMB on KIPAC's website »KIPAC's BICEP page »KIPAC's Keck Array page »