In 1964, two American scientists, Arno Penzias and Robert Wilson were investigating radio signals coming from our galaxy, the Milky way. For this purpose, they were using a giant antenna located in Holmdel, New Jersey. Suddenly the two scientists noticed a strange background noise, similar to the buzzing sound you hear on a radio when it picks up a random signal instead of a clear broadcast signal.

Intrigued by the unexpected sound, the two scientists tried moving the antenna in different directions. But wherever they pointed the antenna, it still picked the sound— even when directed towards empty space. Looking around, they found a pigeon nest inside the antenna— a family of pigeons had setup home in the antenna. The scientists wondered if pigeon poo was causing interference with the signals. They removed the nest and cleared up the poo. But the humming sound still persisted.

Puzzled by the mysterious sound, the two scientists contacted a fellow scientist named Robert Dicke, and invited him to listen the sound. Together, they made an incredible discovery: the sound they were hearing was the leftover radiation right from the beginning of the universe. This leftover radiation was named the Cosmic Microwave Background (CMB) radiation. The discovery of CMB radiation was the primary observational evidence used by scientists to prove the Big Bang Theory.