Cosmic microwave background

type of thermal radiation; cosmic background radiation that is fundamental to observational cosmology because it is the oldest light in the universe, dating to the epoch of recombination

In physical cosmology, the cosmic microwave background (CMB, CMBR) is electromagnetic radiation as a faint, very cold relic from the very early Big Bang. The CMB is also known as the cosmic microwave background radiation (CMBR) or "relic radiation". The radiation of the CMB is everywhere in space and is most detectable in the microwave spectrum.

Full-sky image derived
from nine years of WMAP data


  • It is now clear that astronomers came across indirect manifestations of the CMB long before the 1960s. In 1941, Andrew McKellar discovered cyanide molecules (HCN) in interstellar space. ... As the object of research, McKellar chose absorption lines caused by cyanide molecules in the star 'ε' of Ophiuchis. He concluded that these lines could only be caused by absorption of light by rotating molecules. Relatively simple calculations allowed McKellar to conclude that the excitation of rotational degrees of freedom of cyanide molecules required the presence of external radiation with an effective temperature of 2.3 K. Neither McKellar himself, nor anyone else, suspected that he had stumbled on a manifestation of the cosmic microwave background.
  • ... we know in particular that for the first 380,000 years of the universe it was filled with a fireball. And we know this for sure because we've seen the fireball. In fact we've seen it , and we've take a photograph of it. This is called the cosmic microwave background radiation, but a much better name for it is the Fireball That Filled the Universe When It Was Much Younger.

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