Scientific Context

How did the Universe begin? The prevailing idea is that the Bang of the Big Bang was an early burst of exponential expansion, dubbed inflation. A key prediction of inflation is that it generated gravitational waves. The corresponding ripples in the space-time fabric left an imprint in the polarization of the Cosmic Microwave Background (CMB).

Experiments are making a major step towards this signal by mapping the microwave sky polarization with an unprecedented sensitivity and combination of sky coverage, angular resolution and wavelengths. With its all-sky coverage, Planck is unique for searching the primordial signal on large angular scales. The ground based and balloon-borne experiments benefit from a new generation of large detector arrays and concentrate on small sky patches, which gives them a better sensitivity than Planck on small angular scales. This next generation of experiments will reach the sensitivity necessary to put the first physically interesting limits on the primordial, B-mode, polarization of the CMB. These experiments may show whether the energy scale of inflation predicted by the simplest models is correct.

However, unlike for temperature anisotropies, Galactic foregrounds have larger amplitude than any putative primordial B-mode signal. The signature of cosmic inflation will not be detected, unless contamination associated with the dusty and magnetized interstellar medium in the Galaxy is removed with the required accuracy and confidence.