Two astronomers cleaned pigeon droppings from their antenna and found the Big Bang's afterglow.
In 1964 two radio astronomers at Bell Labs could not get rid of a faint hiss in their antenna. They evicted nesting pigeons and cleaned out their droppings, but it stayed. It was coming from every direction in the sky: the afterglow of the Big Bang. They later won a Nobel Prize.
Arno Penzias and Robert Wilson were using a large horn antenna in Holmdel, New Jersey, originally built for early satellite communication experiments. Their receiver picked up a steady background noise, far stronger than expected, that was the same day and night and in every direction. They were convinced it did not come from Earth, the Sun or our galaxy. After checking the equipment, removing pigeons that had nested in the antenna and cleaning out what they had left behind, the noise remained.
Meanwhile, just down the road at Princeton, Robert Dicke's team was building an instrument to look for exactly this signal. The idea went back to 1948, when Ralph Alpher and Robert Herman predicted that if the universe began hot and dense, the radiation from that era should still be around, stretched by cosmic expansion into microwaves at a few degrees above absolute zero. When Dicke got the call from Bell Labs, he reportedly told his colleagues, 'Boys, we've been scooped.' Penzias and Wilson shared the 1978 Nobel Prize in Physics.
The radiation dates from about 380,000 years after the Big Bang. Before then the universe was a glowing fog of hot plasma that light could not travel through. As it cooled to about 3,000 kelvin, electrons and protons combined into atoms, and the universe turned transparent. The light released then has been travelling ever since, cooling as space expanded, to about 2.725 kelvin today.
It is the key evidence for the Big Bang, and it is astonishingly smooth, uniform to about one part in 25,000. The tiny variations are what matter most. The COBE satellite mapped them in the early 1990s, earning its leaders a Nobel Prize in 2006, and later missions, WMAP and Planck, used the pattern of ripples to measure the universe's shape and contents.
Source: Wikipedia — Cosmic microwave background · Text summarised from Wikipedia (CC BY-SA 4.0)
