The Cosmic Microwave Background

In the past decade, cosmology has undergone a revolution, becoming a precision science. Remarkably, uncertainties in the measurements of the constituents of the Universe and its expansion history have been reduced from factors of few to percent precision in some cases. As a result, we have taken a census of the Universe and learnt much about its evolution. The fossilized heat of the Big Bang, the cosmic microwave background (CMB), has been the foundation for the age of precision cosmology. The most revealing CMB data so far has come from ESA's Planck CMB satellite.

The CMB is a picture of the universe when it was less than 0.01% of its present age.  It carries the almost unblemished signature of primordial fluctuations in the early universe which, under the action of gravitational instability, grew into the remarkable variety of structures that fill the universe today. Given the extreme conditions in the early universe, the CMB is our best hope of uncovering fingerprints of the physics operating at very high energy scales, inaccessible to Earth-bound particle accelerators.