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The cosmic microwave background is electromagnetic radiation throughout the universe, with a temperature of 2.725 K and a wavelength of 1.9 mm. It is evidence of the Big Bang and originated from the universe’s plasma period. It is mostly homogeneous and isotropic, and its spectrum is the most precisely measured black-body spectrum. The COBE satellite took a famous image of its distribution in 1990.
The cosmic microwave background, usually abbreviated CMB, is a form of electromagnetic radiation that permeates the entire universe. It has a temperature of 2.725 K and is in the microwave portion of the spectrum (hence the name), peaking in intensity at a wavelength of 1.9 mm. The cosmic microwave background is sometimes called “the echo of the Big Bang” and is the best current evidence that the universe we live in began as a giant explosion from a point source.
The cosmic microwave background is isotropic to 1 part in 100,000, which means that it varies in intensity only slightly and is mostly homogeneous. This helps indicate that it originated from something that affected the entire universe rather than just a subset of the universe. The cosmic microwave background spectrum has the distinction of being the most precisely measured black-body spectrum in nature.
The cosmic microwave background radiation are photons left over from the extremely energetic time period in the universe for the first million years after the Big Bang. In those days, the entire universe was opaque and made of plasma, like a giant star thousands or millions of light-years in diameter. Eventually, the plasma cooled into neutral atoms, at which point the photons decoupled from the matter and began to move freely through space. The photons have cooled since then and continue to cool from their current temperature of about 2.7 K.
The cosmic microwave background was originally predicted in 1948 by George Gamow and Ralph Alpher, but it wasn’t observed until 1956. The microwave background we observe comes from a spherical surface called the surface of ultimate dispersion, which refers to the point in the past of the universe when photons stopped being scattered by charged matter and began to move freely.
One of the most famous images in cosmology is that of the cosmic microwave background, taken by the COBE satellite in 1990. This shows the distribution of the cosmic microwave background in the sky and reveals its large-scale structure.
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