What is cosmic background radiation?
Let’s define it:
(noun) cosmic background radiation, CBR, cosmic microwave background radiation, CMBR, cosmic microwave background, CMB ((cosmology) the cooled remnant of the hot big bang that fills the entire universe and can be observed today with an average temperature of about 2.725 kelvin)
Universe Today elaborates:
The cosmic background radiation, more commonly called the cosmic microwave background radiation(CMBR) is electromagnetic radiation that fills the Universe. The radiation can only be detected with a radio telescope which makes it show as a faint glow. This glow is strongest in the microwave area of the radio spectrum.
The cosmic background radiation is radiation left over from early development of the universe, and is a landmark proof of the Big Bang theory. Before the formation of stars and planets, the Universe was smaller, much hotter, and filled with a uniform glow from its white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled and stable atoms could form, they eventually could no longer absorb the thermal radiation and the universe became transparent instead of being an opaque fog. The photons that from that time have been propagating ever since, growing fainter and less energetic. The CMBR has a thermal black body spectrum at a temperature of 2.725 K, so it peaks in the microwave range frequency of 160.2 Ghz(1.9 mm wavelength).
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