Cosmic microwave background radiation CMBR

Cosmic microwave background radiation (CMBR) is the oldest light we can see. It is a snapshot of how the universe looked in its early beginnings. First discovered in 1964, CMBR is composed of photons which we can see because of the atoms that formed when the universe cooled to 3000 K. Prior to that, after the Big Bang, the universe was so hot that the photons were scattered all over the universe, making the universe opaque. The atoms caused the photons to scatter less and the universe to become transparent to radiation. Since cooling to 3000K, the universe has continued to expand and cool. 

The information concerning the constitution of the early Universe has increased tremendously during the past decade, mainly due to improved observations of the cosmic microwave background radiation (CMBR). The most important cosmological parameters (the total energy density, the part contained in baryonic matter, the part of nonbaryonic dark matter (DM), other components, etc.) have been determined with percent level accuracy as a result of projects completed in the first decade of the twenty-first century and now appear in tables of fundamental physical data (Amsler et al. 2008). 

Stochastic gravitational waves from the early universe. Can be detected as anisotropies of the Cosmic Microwave Background Radiation (CMBR). Waves from the big bang may be parametrically amplified by inflation. 

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