An excellent article describing the predictions of a CMB, its subsequent discovery and its usefulness in learning about the universe:-http://phys.org/news/2015-07-accidental-discovery-key-universe.html-"Penzias and Wilson were working with a very sensitive radio telescope at Bell Labs in New Jersey, looking for something completely different - neutral hydrogen - when they happened to stumble upon a strange signal from their telescope.-"In order to detect such a faint signal, they needed to make sure they knew the source of every part of the signal their telescope was detecting. As such, they had to account for a number of peculiar things, such as badly insulated wires and even pigeon droppings in the horn of the antenna.-"There was one part of the signal, however, that they could not eliminate. It was there day and night, throughout the year, and appeared wherever they were pointing their antenna. They were completely perplexed as to what it was, until Penzias ran into Bernard Burke, a radio astronomer working at the Department for Terrestrial Magnetism in Washington DC, on an aeroplane who urged him to phone Bob Dicke at Princeton University.-"Dicke and his team were actually looking for the CMB, as their theoretical models suggested that a young, hot, dense universe would produce such radiation. They were months away from making their own measurements but Penzias and Wilson got there first. Dicke came off the phone to Penzias and said to his colleagues: "Boys, we've been scooped."-"Their discovery was published in the July issue of the Astrophysical Journal with one of the most understated titles in the history of physics: "A measurement of excess antenna temperature at 4080 Mc/s". But hidden behind these words was one of the most important discoveries in the history of science - the first direct evidence that the universe had begun with the Big Bang.-"It turns out the CMB had already been predicted in 1948 by a team led by Russian theoretician George Gamow. Dicke was unaware of this work when he published in 1965, so when the paper appeared, Gamow wrote to Dicke pointing out his team's earlier work, and from that point on the two teams have been jointly credited with the prediction. In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint discovery of the CMB; neither Dicke nor Gamow got anything."-***-"In the 50 years since its first discovery, it is no exaggeration to say that we have learnt more about the properties of the universe by studying the CMB than we have from any other single type of observation. Its first discovery in July 1965 is truly one of the landmarks of 20th century science."