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Cosmic microwave background radiation facts for kids

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WMAP 2010
The cosmic microwave background (CMB) temperature fluctuations from the 7-year Wilkinson Microwave Anisotropy Probe data seen over the full sky. The image is a projection of the temperature variations over the celestial sphere. The average temperature is 2.725 Kelvin above absolute zero (absolute zero is equivalent to -273.15 ºC or -459 ºF), and the colors represent the tiny temperature fluctuations, as in a weather map. Red regions are warmer and blue regions are colder by about 0.0002 degrees

The cosmic microwave background (CMB or CMBR) is microwave radiation that fills all space in the observable universe. It was first detected by Arno Penzias and Robert Wilson.

With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. So scientists believe it comes from our earliest infant universe.

The existence of CMB radiation is important evidence that the Big Bang theory is true.

During the Big Bang, a lot of high-energy radiation was created. Then, the universe became bigger and colder. Therefore, the high-energy photons lost most of their original energy. Now, as a result, that radiation is in the microwave part of the electromagnetic spectrum (the microwave part has quite low energy). It has been traveling without hitting anything ever since the time the universe became transparent, about 380,000 years after the Big Bang.

On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background. The map suggests the universe is slightly older than researchers expected. According to the data, the age of the universe is 13.799±0.021 billion years old.


The cosmic microwave background was first predicted in 1948 by Ralph Alpher and Robert Herman.

Horn Antenna-in Holmdel, New Jersey - restoration1
The Holmdel Horn Antenna on which Penzias and Wilson discovered the cosmic microwave background. The antenna was constructed in 1959 to support Project Echo—the National Aeronautics and Space Administration's passive communications satellites, which used large earth orbiting aluminized plastic balloons as reflectors to bounce radio signals from one point on the Earth to another.

The first published recognition of the CMB radiation as a detectable phenomenon appeared in a brief paper by Soviet astrophysicists A. G. Doroshkevich and Igor Novikov, in the spring of 1964. In 1964, David Todd Wilkinson and Peter Roll, Dicke's colleagues at Princeton University, began constructing a Dicke radiometer to measure the cosmic microwave background. In 1964, Arno Penzias and Robert Woodrow Wilson at the Crawford Hill location of Bell Telephone Laboratories in nearby Holmdel Township, New Jersey had built a Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments. On 20 May 1964 they made their first measurement clearly showing the presence of the microwave background, with their instrument having an excess 4.2K antenna temperature which they could not account for. After receiving a telephone call from Crawford Hill, Dicke said "Boys, we've been scooped." A meeting between the Princeton and Crawford Hill groups determined that the antenna temperature was indeed due to the microwave background. Penzias and Wilson received the 1978 Nobel Prize in Physics for their discovery.

Future evolution

Assuming the universe keeps expanding and it does not suffer a Big Crunch, a Big Rip, or another similar fate, the cosmic microwave background will continue redshifting until it will no longer be detectable, and will be superseded first by the one produced by starlight, and perhaps, later by the background radiation fields of processes that may take place in the far future of the universe such as proton decay, evaporation of black holes, and positronium decay.

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See also

Kids robot.svg In Spanish: Radiación de fondo de microondas para niños

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