Primordial Background Radiation (or Cosmic Microwave Background)

One of the strongest pieces of evidence in support of the Standard Hot Big Bang Model is the 2.7 degree Kelvin radiation seen in all directions, discovered by Arno Penzias and Robert Wilson in 1965.

Using a special "horn" radio antenna, Penzias and Wilson found an unidentified source of radio emission that seemed to be the same in all directions. When they measured its spectrum, they discovered that it perfectly fit the Planck curve (the variation in brightness with wavelength) from a thermal blackbody source with a temperature of 2.7 degrees Kelvin.

At about the same time, Robert Dicke was proposing to search for the thermal remnant of the Big Bang predicted by George Gamow to resemble a blackbody of less than 10 degrees Kelvin. When Penzias and Wilson learned of Dicke's proposition, they realized that they had already made the discovery.

The 1978 Nobel Prize in Physics was partly awarded to Penzias and Wilson for their discovery.

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