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.
